diff --git a/spec/std/time/time_spec.cr b/spec/std/time/time_spec.cr
index 8c80d5e6f1de..74a6f3031e08 100644
--- a/spec/std/time/time_spec.cr
+++ b/spec/std/time/time_spec.cr
@@ -651,18 +651,18 @@ describe Time do
   end
 
   it "#inspect" do
-    Time.utc(2014, 1, 2, 3, 4, 5).inspect.should eq "2014-01-02 03:04:05.0 UTC"
-    Time.utc(2014, 1, 2, 3, 4, 5, nanosecond: 123_456_789).inspect.should eq "2014-01-02 03:04:05.123456789 UTC"
+    Time.utc(2014, 1, 2, 3, 4, 5).inspect.should eq "2014-01-02 03:04:05Z"
+    Time.utc(2014, 1, 2, 3, 4, 5, nanosecond: 123_456_789).inspect.should eq "2014-01-02 03:04:05.123456789Z"
 
     with_zoneinfo do
       location = Time::Location.load("Europe/Berlin")
-      Time.local(2014, 1, 2, 3, 4, 5, location: location).inspect.should eq "2014-01-02 03:04:05.0 +01:00 Europe/Berlin"
-      Time.local(2014, 1, 2, 3, 4, 5, nanosecond: 123_456_789, location: location).inspect.should eq "2014-01-02 03:04:05.123456789 +01:00 Europe/Berlin"
+      Time.local(2014, 1, 2, 3, 4, 5, location: location).inspect.should eq "2014-01-02 03:04:05+01:00[Europe/Berlin]"
+      Time.local(2014, 1, 2, 3, 4, 5, nanosecond: 123_456_789, location: location).inspect.should eq "2014-01-02 03:04:05.123456789+01:00[Europe/Berlin]"
     end
 
     location = Time::Location.fixed(3601)
-    Time.local(2014, 1, 2, 3, 4, 5, location: location).inspect.should eq "2014-01-02 03:04:05.0 +01:00:01"
-    Time.local(2014, 1, 2, 3, 4, 5, nanosecond: 123_456_789, location: location).inspect.should eq "2014-01-02 03:04:05.123456789 +01:00:01"
+    Time.local(2014, 1, 2, 3, 4, 5, location: location).inspect.should eq "2014-01-02 03:04:05+01:00:01"
+    Time.local(2014, 1, 2, 3, 4, 5, nanosecond: 123_456_789, location: location).inspect.should eq "2014-01-02 03:04:05.123456789+01:00:01"
   end
 
   it "at methods" do
diff --git a/src/file.cr b/src/file.cr
index 0a218bcf91ec..63cbf9f17d87 100644
--- a/src/file.cr
+++ b/src/file.cr
@@ -40,7 +40,7 @@ require "crystal/system/file"
 # tempfile = File.tempfile("foo")
 #
 # File.size(tempfile.path)                   # => 6
-# File.info(tempfile.path).modification_time # => 2015-10-20 13:11:12 UTC
+# File.info(tempfile.path).modification_time # => 2015-10-20 13:11:12Z
 # File.exists?(tempfile.path)                # => true
 # File.read_lines(tempfile.path)             # => ["foobar"]
 # ```
@@ -208,7 +208,7 @@ class File < IO::FileDescriptor
   # ```
   # File.write("foo", "foo")
   # File.info("foo").size              # => 3
-  # File.info("foo").modification_time # => 2015-09-23 06:24:19 UTC
+  # File.info("foo").modification_time # => 2015-09-23 06:24:19Z
   #
   # File.symlink("foo", "bar")
   # File.info("bar", follow_symlinks: false).type.symlink? # => true
diff --git a/src/http/common.cr b/src/http/common.cr
index b82455d1df54..66963e669fe1 100644
--- a/src/http/common.cr
+++ b/src/http/common.cr
@@ -343,9 +343,9 @@ module HTTP
   # ```
   # require "http"
   #
-  # HTTP.parse_time("Sun, 14 Feb 2016 21:00:00 GMT")  # => "2016-02-14 21:00:00 UTC"
-  # HTTP.parse_time("Sunday, 14-Feb-16 21:00:00 GMT") # => "2016-02-14 21:00:00 UTC"
-  # HTTP.parse_time("Sun Feb 14 21:00:00 2016")       # => "2016-02-14 21:00:00 UTC"
+  # HTTP.parse_time("Sun, 14 Feb 2016 21:00:00 GMT")  # => "2016-02-14 21:00:00Z"
+  # HTTP.parse_time("Sunday, 14-Feb-16 21:00:00 GMT") # => "2016-02-14 21:00:00Z"
+  # HTTP.parse_time("Sun Feb 14 21:00:00 2016")       # => "2016-02-14 21:00:00Z"
   # ```
   #
   # Uses `Time::Format::HTTP_DATE` as parser.
diff --git a/src/json/to_json.cr b/src/json/to_json.cr
index b4d0881f79e9..979709de7adf 100644
--- a/src/json/to_json.cr
+++ b/src/json/to_json.cr
@@ -310,7 +310,7 @@ end
 # end
 #
 # timestamp = TimestampArray.from_json(%({"dates":[1459859781,1567628762]}))
-# timestamp.dates   # => [2016-04-05 12:36:21 UTC, 2019-09-04 20:26:02 UTC]
+# timestamp.dates   # => [2016-04-05 12:36:21Z, 2019-09-04 20:26:02Z]
 # timestamp.to_json # => %({"dates":[1459859781,1567628762]})
 # ```
 #
@@ -328,7 +328,7 @@ end
 # end
 #
 # timestamp = TimestampArray.from_json(%({"dates":["Apr 5, 2016","Sep 4, 2019"]}))
-# timestamp.dates   # => [2016-04-05 00:00:00 UTC, 2019-09-04 00:00:00 UTC]
+# timestamp.dates   # => [2016-04-05 00:00:00Z, 2019-09-04 00:00:00Z]
 # timestamp.to_json # => %({"dates":["Apr 5, 2016","Sep 4, 2019"]})
 # ```
 #
@@ -371,7 +371,7 @@ end
 # end
 #
 # timestamp = TimestampHash.from_json(%({"birthdays":{"foo":1459859781,"bar":1567628762}}))
-# timestamp.birthdays # => {"foo" => 2016-04-05 12:36:21 UTC, "bar" => 2019-09-04 20:26:02 UTC}
+# timestamp.birthdays # => {"foo" => 2016-04-05 12:36:21Z, "bar" => 2019-09-04 20:26:02Z}
 # timestamp.to_json   # => %({"birthdays":{"foo":1459859781,"bar":1567628762}})
 # ```
 #
@@ -389,7 +389,7 @@ end
 # end
 #
 # timestamp = TimestampHash.from_json(%({"birthdays":{"foo":"Apr 5, 2016","bar":"Sep 4, 2019"}}))
-# timestamp.birthdays # => {"foo" => 2016-04-05 00:00:00 UTC, "bar" => 2019-09-04 00:00:00 UTC}
+# timestamp.birthdays # => {"foo" => 2016-04-05 00:00:00Z, "bar" => 2019-09-04 00:00:00Z}
 # timestamp.to_json   # => %({"birthdays":{"foo":"Apr 5, 2016","bar":"Sep 4, 2019"}})
 # ```
 #
@@ -435,7 +435,7 @@ end
 # end
 #
 # person = Person.from_json(%({"birth_date": 1459859781}))
-# person.birth_date # => 2016-04-05 12:36:21 UTC
+# person.birth_date # => 2016-04-05 12:36:21Z
 # person.to_json    # => %({"birth_date":1459859781})
 # ```
 module Time::EpochConverter
@@ -459,7 +459,7 @@ end
 # end
 #
 # timestamp = Timestamp.from_json(%({"value": 1459860483856}))
-# timestamp.value   # => 2016-04-05 12:48:03.856 UTC
+# timestamp.value   # => 2016-04-05 12:48:03.856Z
 # timestamp.to_json # => %({"value":1459860483856})
 # ```
 module Time::EpochMillisConverter
diff --git a/src/time.cr b/src/time.cr
index 081114b1e0dc..d1e94571f227 100644
--- a/src/time.cr
+++ b/src/time.cr
@@ -9,7 +9,7 @@ require "crystal/system/time"
 # Leap seconds are ignored.
 #
 # Internally, the time is stored as an `Int64` representing seconds from epoch
-# (`0001-01-01 00:00:00.0 UTC`) and an `Int32` representing
+# (`0001-01-01 00:00:00Z`) and an `Int32` representing
 # nanosecond-of-second with value range `0..999_999_999`.
 #
 # The supported date range is `0001-01-01 00:00:00.0` to
@@ -84,7 +84,7 @@ require "crystal/system/time"
 #
 # ```
 # time = Time.local(2018, 3, 8, 22, 5, 13, location: Time::Location.load("Europe/Berlin"))
-# time          # => 2018-03-08 22:05:13 +01:00 Europe/Berlin
+# time          # => 2018-03-08 22:05:13+01:00[Europe/Berlin]
 # time.location # => #<Time::Location Europe/Berlin>
 # time.zone     # => #<Time::Location::Zone CET +01:00 (3600s) STD>
 # time.offset   # => 3600
@@ -94,7 +94,7 @@ require "crystal/system/time"
 #
 # ```
 # time = Time.utc(2018, 3, 8, 22, 5, 13)
-# time          # => 2018-03-08 22:05:13.0 UTC
+# time          # => 2018-03-08 22:05:13Z
 # time.location # => #<Time::Location UTC>
 # time.zone     # => #<Time::Location::Zone UTC +00:00 (0s) STD>
 # time.offset   # => 0
@@ -106,8 +106,8 @@ require "crystal/system/time"
 # ```
 # time_de = Time.local(2018, 3, 8, 22, 5, 13, location: Time::Location.load("Europe/Berlin"))
 # time_ar = time_de.in Time::Location.load("America/Argentina/Buenos_Aires")
-# time_de # => 2018-03-08 22:05:13 +01:00 Europe/Berlin
-# time_ar # => 2018-03-08 18:05:13 -03:00 America/Argentina/Buenos_Aires
+# time_de # => 2018-03-08 22:05:13+01:00[Europe/Berlin]
+# time_ar # => 2018-03-08 18:05:13-03:00[America/Argentina/Buenos_Aires]
 # ```
 #
 # Both `Time` instances show a different local date-time, but they represent
@@ -115,8 +115,8 @@ require "crystal/system/time"
 # equal:
 #
 # ```
-# time_de.to_utc     # => 2018-03-08 21:05:13 UTC
-# time_ar.to_utc     # => 2018-03-08 21:05:13 UTC
+# time_de.to_utc     # => 2018-03-08 21:05:13Z
+# time_ar.to_utc     # => 2018-03-08 21:05:13Z
 # time_de == time_ar # => true
 # ```
 #
@@ -267,7 +267,7 @@ struct Time
   # :nodoc:
   DAYS_PER_4_YEARS = 365*4 + 1
 
-  # This constant is defined to be "1970-01-01 00:00:00 UTC".
+  # This constant is defined as `1970-01-01 00:00:00Z`".
   # Can be used to create a `Time::Span` that represents an Unix Epoch time duration.
   #
   # ```
@@ -379,7 +379,7 @@ struct Time
   #
   # ```
   # time = Time.local(2016, 2, 15, 10, 20, 30, location: Time::Location.load("Europe/Berlin"))
-  # time.inspect # => "2016-02-15 10:20:30.0 +01:00 Europe/Berlin"
+  # time.inspect # => "2016-02-15 10:20:30+01:00[Europe/Berlin]"
   # ```
   #
   # Valid value ranges for the individual fields:
@@ -470,7 +470,7 @@ struct Time
   end
 
   # Creates a new `Time` instance that corresponds to the number of *seconds*
-  # and *nanoseconds* elapsed from epoch (`0001-01-01 00:00:00.0 UTC`)
+  # and *nanoseconds* elapsed from epoch (`0001-01-01 00:00:00.0`)
   # observed in *location*.
   #
   # Valid range for *seconds* is `0..315_537_897_599`.
@@ -493,7 +493,7 @@ struct Time
   end
 
   # Creates a new `Time` instance that corresponds to the number of *seconds*
-  # and *nanoseconds* elapsed from epoch (`0001-01-01 00:00:00.0 UTC`)
+  # and *nanoseconds* elapsed from epoch (`0001-01-01 00:00:00Z`)
   # in UTC.
   #
   # Valid range for *seconds* is `0..315_537_897_599`.
@@ -512,24 +512,24 @@ struct Time
   {% end %}
 
   # Creates a new `Time` instance that corresponds to the number of
-  # *seconds* elapsed since the Unix epoch (`1970-01-01 00:00:00 UTC`).
+  # *seconds* elapsed since the Unix epoch (`1970-01-01 00:00:00Z`).
   #
   # The time zone is always UTC.
   #
   # ```
-  # Time.unix(981173106) # => 2001-02-03 04:05:06 UTC
+  # Time.unix(981173106) # => 2001-02-03 04:05:06Z
   # ```
   def self.unix(seconds : Int) : Time
     utc(seconds: UNIX_EPOCH.total_seconds + seconds, nanoseconds: 0)
   end
 
   # Creates a new `Time` instance that corresponds to the number of
-  # *milliseconds* elapsed since the Unix epoch (`1970-01-01 00:00:00 UTC`).
+  # *milliseconds* elapsed since the Unix epoch (`1970-01-01 00:00:00Z`).
   #
   # The time zone is always UTC.
   #
   # ```
-  # time = Time.unix_ms(981173106789) # => 2001-02-03 04:05:06.789 UTC
+  # time = Time.unix_ms(981173106789) # => 2001-02-03 04:05:06.789Z
   # time.millisecond                  # => 789
   # ```
   def self.unix_ms(milliseconds : Int) : Time
@@ -540,12 +540,12 @@ struct Time
   end
 
   # Creates a new `Time` instance that corresponds to the number of
-  # *nanoseconds* elapsed since the Unix epoch (`1970-01-01 00:00:00.000000000 UTC`).
+  # *nanoseconds* elapsed since the Unix epoch (`1970-01-01 00:00:00Z`).
   #
   # The time zone is always UTC.
   #
   # ```
-  # time = Time.unix_ns(981173106789479273) # => 2001-02-03 04:05:06.789479273 UTC
+  # time = Time.unix_ns(981173106789479273) # => 2001-02-03 04:05:06.789479273Z
   # time.nanosecond                         # => 789479273
   # ```
   def self.unix_ns(nanoseconds : Int) : Time
@@ -566,8 +566,8 @@ struct Time
   # new_year = Time.utc(2019, 1, 1, 0, 0, 0)
   # tokyo = new_year.to_local_in(Time::Location.load("Asia/Tokyo"))
   # new_york = new_year.to_local_in(Time::Location.load("America/New_York"))
-  # tokyo.inspect    # => "2019-01-01 00:00:00.0 +09:00 Asia/Tokyo"
-  # new_york.inspect # => "2019-01-01 00:00:00.0 -05:00 America/New_York"
+  # tokyo.inspect    # => "2019-01-01 00:00:00+09:00[Asia/Tokyo]"
+  # new_york.inspect # => "2019-01-01 00:00:00-05:00[America/New_York]"
   # ```
   #
   # If the given wall clock is a gap or fold in the target location, no
@@ -582,10 +582,10 @@ struct Time
   # nyc = Time::Location.load("America/New_York")
   #
   # # gap on 2025-03-09 local time: 02:00:00 STD -> 03:00:00 DST
-  # Time.utc(2025, 3, 9, 2, 12, 34).to_local_in(nyc) # => 2025-03-09 01:12:34.0 -05:00 America/New_York
+  # Time.utc(2025, 3, 9, 2, 12, 34).to_local_in(nyc) # => 2025-03-09 01:12:34.0-05:00[America/New_York]
   #
   # # overlap on 2025-11-02 local time: 02:00:00 DST -> 01:00:00 STD
-  # Time.utc(2025, 11, 2, 1, 12, 34).to_local_in(nyc) # => 2025-11-02 01:12:34.0 -04:00 America/New_York
+  # Time.utc(2025, 11, 2, 1, 12, 34).to_local_in(nyc) # => 2025-11-02 01:12:34.0-04:00[America/New_York]
   # ```
   def to_local_in(location : Location) : Time
     local_seconds = offset_seconds
@@ -1046,8 +1046,8 @@ struct Time
   # time_de == time_ar # => true
   #
   # # both times represent the same instant:
-  # time_de.to_utc # => 2018-03-08 21:05:13 UTC
-  # time_ar.to_utc # => 2018-03-08 21:05:13 UTC
+  # time_de.to_utc # => 2018-03-08 21:05:13Z
+  # time_ar.to_utc # => 2018-03-08 21:05:13Z
   # ```
   def ==(other : Time) : Bool
     total_seconds == other.total_seconds && nanosecond == other.nanosecond
@@ -1098,29 +1098,29 @@ struct Time
 
   # Prints this `Time` to *io*.
   #
-  # The local date-time is formatted as date string `YYYY-MM-DD HH:mm:ss.nnnnnnnnn +ZZ:ZZ:ZZ`.
-  # Nanoseconds are omitted if *with_nanoseconds* is `false`.
-  # When the location is `UTC`, the offset is omitted. Offset seconds are omitted if `0`.
+  # It's formatted according to the Internet Extended Date/Time Format (IXDTF)
+  # as specified in [RFC 9557](https://datatracker.ietf.org/doc/html/rfc9557):
+  # An [RFC 3339](https://tools.ietf.org/html/rfc3339) formatted local date-time
+  # string with nanosecond precision followed by a time zone name suffix.
   #
-  # The name of the location is appended unless it is a fixed zone offset.
+  # It is similar to the format `%FT%T.%N%::z[%Z]`. Some parts may be omitted or
+  # shortened.
+  #
+  # Nanoseconds are omitted if *with_nanoseconds* is `false` or `nanoseconds`
+  # are zero. Zero offset seconds are omitted.  The name of the location is
+  # omitted for fixed zone offset.
+  #
+  # ```
+  # Time.utc(2014, 1, 2, 3, 4, 5)                      # => 2014-01-02 03:04:05Z
+  # Time.utc(2014, 1, 2, 3, 4, 5, nanosecond: 123_456) # => 2014-01-02 03:04:05.123456000Z
+  #
+  # Time.local(2014, 1, 2, 3, 4, 5, location: Time::Location.load("Europe/Berlin")) # => 2014-01-02 03:04:05+01:00[Europe/Berlin]
+  # Time.local(2014, 1, 2, 3, 4, 5, location: Time::Location.fixed(3600))           # => 2014-01-02 03:04:05+01:00
+  # Time.local(2014, 1, 2, 3, 4, 5, location: Time::Location.fixed(3601))           # => 2014-01-02 03:04:05+01:00:01
+  # ```
   def inspect(io : IO, with_nanoseconds = true) : Nil
-    to_s io, "%F %T"
-
-    if with_nanoseconds
-      if @nanoseconds == 0
-        io << ".0"
-      else
-        to_s io, ".%N"
-      end
-    end
-
-    if utc?
-      io << " UTC"
-    else
-      io << ' '
-      zone.format(io)
-      io << ' ' << location.name unless location.fixed?
-    end
+    Format::RFC_3339.format(self, io, fraction_digits: (with_nanoseconds && !nanosecond.zero?) ? 9 : 0, preferred_separator: ' ')
+    io << '[' << location.name << ']' unless location.fixed?
   end
 
   # Prints this `Time` to *io*.
@@ -1165,7 +1165,7 @@ struct Time
   # Format this time using the format specified by [RFC 3339](https://tools.ietf.org/html/rfc3339) ([ISO 8601](https://web.archive.org/web/20250306154328/http://xml.coverpages.org/ISO-FDIS-8601.pdf) profile).
   #
   # ```
-  # Time.utc(2016, 2, 15).to_rfc3339 # => "2016-02-15T00:00:00Z"
+  # Time.utc(2016, 2, 15).to_rfc3339 # => "2016-02-15 00:00:00Z"
   # ```
   #
   # ISO 8601 allows some freedom over the syntax and RFC 3339 exercises that
@@ -1191,7 +1191,7 @@ struct Time
   # Parse time format specified by [RFC 3339](https://tools.ietf.org/html/rfc3339) ([ISO 8601](https://web.archive.org/web/20250306154328/http://xml.coverpages.org/ISO-FDIS-8601.pdf) profile).
   #
   # ```
-  # Time.parse_rfc3339("2016-02-15T04:35:50Z") # => 2016-02-15 04:35:50.0 UTC
+  # Time.parse_rfc3339("2016-02-15T04:35:50Z") # => 2016-02-15 04:35:50Z
   # ```
   def self.parse_rfc3339(time : String) : self
     Format::RFC_3339.parse(time)
@@ -1205,7 +1205,7 @@ struct Time
   # Use `#to_rfc3339` to format a `Time` according to .
   #
   # ```
-  # Time.parse_iso8601("2016-02-15T04:35:50Z") # => 2016-02-15 04:35:50.0 UTC
+  # Time.parse_iso8601("2016-02-15T04:35:50Z") # => 2016-02-15 04:35:50Z
   # ```
   def self.parse_iso8601(time : String)
     Format::ISO_8601_DATE_TIME.parse(time)
@@ -1235,7 +1235,7 @@ struct Time
   # This is also compatible to [RFC 882](https://tools.ietf.org/html/rfc882) and [RFC 1123](https://tools.ietf.org/html/rfc1123#page-55).
   #
   # ```
-  # Time.parse_rfc2822("Mon, 15 Feb 2016 04:35:50 UTC") # => 2016-02-15 04:35:50.0 UTC
+  # Time.parse_rfc2822("Mon, 15 Feb 2016 04:35:50 UTC") # => 2016-02-15 04:35:50Z
   # ```
   def self.parse_rfc2822(time : String) : self
     Format::RFC_2822.parse(time)
@@ -1246,7 +1246,7 @@ struct Time
   # See `Time::Format` for details.
   #
   # ```
-  # Time.parse("2016-04-05", "%F", Time::Location.load("Europe/Berlin")) # => 2016-04-05 00:00:00.0 +02:00 Europe/Berlin
+  # Time.parse("2016-04-05", "%F", Time::Location.load("Europe/Berlin")) # => 2016-04-05 00:00:00+02:00[Europe/Berlin]
   # ```
   #
   # If there is no time zone information in the formatted time, *location* will
@@ -1304,7 +1304,7 @@ struct Time
   end
 
   # Returns the number of seconds since the Unix epoch
-  # (`1970-01-01 00:00:00 UTC`).
+  # (`1970-01-01 00:00:00Z`).
   #
   # ```
   # time = Time.utc(2016, 1, 12, 3, 4, 5)
@@ -1315,7 +1315,7 @@ struct Time
   end
 
   # Returns the number of milliseconds since the Unix epoch
-  # (`1970-01-01 00:00:00 UTC`).
+  # (`1970-01-01 00:00:00Z`).
   #
   # ```
   # time = Time.utc(2016, 1, 12, 3, 4, 5, nanosecond: 678_000_000)
@@ -1326,7 +1326,7 @@ struct Time
   end
 
   # Returns the number of nanoseconds since the Unix epoch
-  # (`1970-01-01 00:00:00.000000000 UTC`).
+  # (`1970-01-01 00:00:00Z`).
   #
   # ```
   # time = Time.utc(2016, 1, 12, 3, 4, 5, nanosecond: 678_910_123)
@@ -1337,7 +1337,7 @@ struct Time
   end
 
   # Returns the number of seconds since the Unix epoch
-  # (`1970-01-01 00:00:00 UTC`) as `Float64` with nanosecond precision.
+  # (`1970-01-01 00:00:00Z`) as `Float64` with nanosecond precision.
   #
   # ```
   # time = Time.utc(2016, 1, 12, 3, 4, 5, nanosecond: 678_000_000)
@@ -1360,8 +1360,8 @@ struct Time
   # ```
   # time_de = Time.local(2018, 3, 8, 22, 5, 13, location: Time::Location.load("Europe/Berlin"))
   # time_ar = time_de.in Time::Location.load("America/Argentina/Buenos_Aires")
-  # time_de # => 2018-03-08 22:05:13 +01:00 Europe/Berlin
-  # time_ar # => 2018-03-08 18:05:13 -03:00 America/Argentina/Buenos_Aires
+  # time_de # => 2018-03-08 22:05:13+01:00[Europe/Berlin]
+  # time_ar # => 2018-03-08 18:05:13-03:00[America/Argentina/Buenos_Aires]
   # ```
   #
   # In contrast, `#to_local_in` changes to a different location while
@@ -1445,9 +1445,9 @@ struct Time
   #
   # ```
   # now = Time.utc(2023, 5, 16, 17, 53, 22)
-  # now.at_beginning_of_week             # => 2023-05-15 00:00:00 UTC
-  # now.at_beginning_of_week(:sunday)    # => 2023-05-14 00:00:00 UTC
-  # now.at_beginning_of_week(:wednesday) # => 2023-05-10 00:00:00 UTC
+  # now.at_beginning_of_week             # => 2023-05-15 00:00:00Z
+  # now.at_beginning_of_week(:sunday)    # => 2023-05-14 00:00:00Z
+  # now.at_beginning_of_week(:wednesday) # => 2023-05-10 00:00:00Z
   # ```
   # TODO: Ensure correctness in local time-line.
   def at_beginning_of_week(start_day : Time::DayOfWeek = :monday) : Time
diff --git a/src/time/format/custom/http_date.cr b/src/time/format/custom/http_date.cr
index 25847b21aa00..dd2268f5b760 100644
--- a/src/time/format/custom/http_date.cr
+++ b/src/time/format/custom/http_date.cr
@@ -10,10 +10,10 @@ struct Time::Format
   # * [asctime](http://en.cppreference.com/w/c/chrono/asctime)
   #
   # ```
-  # Time::Format::HTTP_DATE.parse("Sun, 14 Feb 2016 21:00:00 GMT")  # => 2016-02-14 21:00:00 UTC
-  # Time::Format::HTTP_DATE.parse("Sunday, 14-Feb-16 21:00:00 GMT") # => 2016-02-14 21:00:00 UTC
-  # Time::Format::HTTP_DATE.parse("Sun, 14-Feb-2016 21:00:00 GMT")  # => 2016-02-14 21:00:00 UTC
-  # Time::Format::HTTP_DATE.parse("Sun Feb 14 21:00:00 2016")       # => 2016-02-14 21:00:00 UTC
+  # Time::Format::HTTP_DATE.parse("Sun, 14 Feb 2016 21:00:00 GMT")  # => 2016-02-14 21:00:00Z
+  # Time::Format::HTTP_DATE.parse("Sunday, 14-Feb-16 21:00:00 GMT") # => 2016-02-14 21:00:00Z
+  # Time::Format::HTTP_DATE.parse("Sun, 14-Feb-2016 21:00:00 GMT")  # => 2016-02-14 21:00:00Z
+  # Time::Format::HTTP_DATE.parse("Sun Feb 14 21:00:00 2016")       # => 2016-02-14 21:00:00Z
   #
   # Time::Format::HTTP_DATE.format(Time.utc(2016, 2, 15)) # => "Mon, 15 Feb 2016 00:00:00 GMT"
   # ```
diff --git a/src/time/format/custom/iso_8601.cr b/src/time/format/custom/iso_8601.cr
index b6e634c7a4de..8da6ce6b06ac 100644
--- a/src/time/format/custom/iso_8601.cr
+++ b/src/time/format/custom/iso_8601.cr
@@ -118,7 +118,7 @@ struct Time::Format
   # The ISO 8601 date format.
   #
   # ```
-  # Time::Format::ISO_8601_DATE.parse("2016-02-15")                      # => 2016-02-15 00:00:00.0 UTC
+  # Time::Format::ISO_8601_DATE.parse("2016-02-15")                      # => 2016-02-15 00:00:00Z
   # Time::Format::ISO_8601_DATE.format(Time.utc(2016, 2, 15, 4, 35, 50)) # => "2016-02-15"
   # ```
   module ISO_8601_DATE
@@ -147,8 +147,8 @@ struct Time::Format
   # The ISO 8601 date time format.
   #
   # ```
-  # Time::Format::ISO_8601_DATE_TIME.format(Time.utc(2016, 2, 15, 4, 35, 50)) # => "2016-02-15T04:35:50Z"
-  # Time::Format::ISO_8601_DATE_TIME.parse("2016-02-15T04:35:50Z")            # => 2016-02-15 04:35:50.0 UTC
+  # Time::Format::ISO_8601_DATE_TIME.format(Time.utc(2016, 2, 15, 4, 35, 50)) # => "2016-02-15 04:35:50Z"
+  # Time::Format::ISO_8601_DATE_TIME.parse("2016-02-15T04:35:50Z")            # => 2016-02-15 04:35:50Z
   # ```
   module ISO_8601_DATE_TIME
     # Parses a string into a `Time`.
@@ -177,7 +177,7 @@ struct Time::Format
   #
   # ```
   # Time::Format::ISO_8601_TIME.format(Time.utc(2016, 2, 15, 4, 35, 50)) # => "04:35:50Z"
-  # Time::Format::ISO_8601_TIME.parse("04:35:50Z")                       # => 0001-01-01 04:35:50.0 UTC
+  # Time::Format::ISO_8601_TIME.parse("04:35:50Z")                       # => 0001-01-01 04:35:50Z
   # ```
   module ISO_8601_TIME
     # Parses a string into a `Time`.
diff --git a/src/time/format/custom/rfc_2822.cr b/src/time/format/custom/rfc_2822.cr
index 3397cce8e471..43236d616fd1 100644
--- a/src/time/format/custom/rfc_2822.cr
+++ b/src/time/format/custom/rfc_2822.cr
@@ -7,7 +7,7 @@ struct Time::Format
   # Time::Format::RFC_2822.format(Time.utc(2016, 2, 15, 4, 35, 50)) # => "Mon, 15 Feb 2016 04:35:50 +0000"
   #
   # Time::Format::RFC_2822.parse("Mon, 15 Feb 2016 04:35:50 +0000") # => 2016-02-15 04:35:50.0 +00:00
-  # Time::Format::RFC_2822.parse("Mon, 15 Feb 2016 04:35:50 UTC")   # => 2016-02-15 04:35:50.0 UTC
+  # Time::Format::RFC_2822.parse("Mon, 15 Feb 2016 04:35:50 UTC")   # => 2016-02-15 04:35:50Z
   # ```
   module RFC_2822
     # Parses a string into a `Time`.
diff --git a/src/time/format/custom/rfc_3339.cr b/src/time/format/custom/rfc_3339.cr
index 3295d9ecacaf..37b35c780797 100644
--- a/src/time/format/custom/rfc_3339.cr
+++ b/src/time/format/custom/rfc_3339.cr
@@ -4,8 +4,8 @@ struct Time::Format
   # ```
   # Time::Format::RFC_3339.format(Time.utc(2016, 2, 15, 4, 35, 50)) # => "2016-02-15T04:35:50Z"
   #
-  # Time::Format::RFC_3339.parse("2016-02-15T04:35:50Z") # => 2016-02-15 04:35:50.0 UTC
-  # Time::Format::RFC_3339.parse("2016-02-15 04:35:50Z") # => 2016-02-15 04:35:50.0 UTC
+  # Time::Format::RFC_3339.parse("2016-02-15T04:35:50Z") # => 2016-02-15 04:35:50Z
+  # Time::Format::RFC_3339.parse("2016-02-15 04:35:50Z") # => 2016-02-15 04:35:50Z
   # ```
   module RFC_3339
     # Parses a string into a `Time`.
@@ -16,27 +16,27 @@ struct Time::Format
     end
 
     # Formats a `Time` into the given *io*.
-    def self.format(time : Time, io : IO, fraction_digits = 0)
+    def self.format(time : Time, io : IO, fraction_digits = 0, *, preferred_separator = 'T')
       formatter = Formatter.new(time, io)
-      formatter.rfc_3339(fraction_digits: fraction_digits)
+      formatter.rfc_3339(fraction_digits: fraction_digits, preferred_separator: preferred_separator)
       io
     end
 
     # Formats a `Time` into a `String`.
-    def self.format(time : Time, fraction_digits = 0) : String
+    def self.format(time : Time, fraction_digits = 0, *, preferred_separator = 'T') : String
       String.build do |io|
-        format(time, io, fraction_digits: fraction_digits)
+        format(time, io, fraction_digits: fraction_digits, preferred_separator: preferred_separator)
       end
     end
   end
 
   module Pattern
-    def rfc_3339(fraction_digits = 0)
+    def rfc_3339(fraction_digits = 0, preferred_separator = 'T')
       year_month_day
-      char 'T', 't', ' '
+      char preferred_separator, 'T', 't', ' '
       twenty_four_hour_time_with_seconds
       second_fraction?(fraction_digits: fraction_digits)
-      time_zone_z_or_offset(force_colon: true)
+      time_zone_z_or_offset(force_colon: true, format_seconds: :auto)
     end
   end
 end
diff --git a/src/time/location.cr b/src/time/location.cr
index 8bc66b9dcfef..4c56db2bbf0b 100644
--- a/src/time/location.cr
+++ b/src/time/location.cr
@@ -18,7 +18,7 @@ require "./location/loader"
 # location = Time::Location.load("Europe/Berlin")
 # location # => #<Time::Location Europe/Berlin>
 # time = Time.local(2016, 2, 15, 21, 1, 10, location: location)
-# time # => 2016-02-15 21:01:10 +01:00 Europe/Berlin
+# time # => 2016-02-15 21:01:10+01:00[Europe/Berlin]
 # ```
 #
 # A custom time zone database can be configured through the environment variable
@@ -447,7 +447,7 @@ class Time::Location
   # Returns the time zone offset observed at *unix_seconds*.
   #
   # *unix_seconds* expresses the number of seconds since UNIX epoch
-  # (`1970-01-01 00:00:00 UTC`).
+  # (`1970-01-01 00:00:00Z`).
   def lookup(unix_seconds : Int) : Zone
     unless @cached_range[0] <= unix_seconds < @cached_range[1]
       @cached_zone, @cached_range = lookup_with_boundaries(unix_seconds)
diff --git a/src/yaml/to_yaml.cr b/src/yaml/to_yaml.cr
index 7c9fdb2c778e..949e81b7db46 100644
--- a/src/yaml/to_yaml.cr
+++ b/src/yaml/to_yaml.cr
@@ -276,7 +276,7 @@ end
 # end
 #
 # timestamp = Timestamp.from_yaml(%({"values":[1459859781,1567628762]}))
-# timestamp.values  # => [2016-04-05 12:36:21 UTC, 2019-09-04 20:26:02 UTC]
+# timestamp.values  # => [2016-04-05 12:36:21Z, 2019-09-04 20:26:02Z]
 # timestamp.to_yaml # => "---\nvalues:\n- 1459859781\n- 1567628762\n"
 # ```
 #
@@ -294,7 +294,7 @@ end
 # end
 #
 # timestamp = Timestamp.from_yaml(%({"values":["Apr 5, 2016","Sep 4, 2019"]}))
-# timestamp.values  # => [2016-04-05 00:00:00 UTC, 2019-09-04 00:00:00 UTC]
+# timestamp.values  # => [2016-04-05 00:00:00Z, 2019-09-04 00:00:00Z]
 # timestamp.to_yaml # => "---\nvalues:\n- Apr 5, 2016\n- Sep 4, 2019\n"
 # ```
 #