diff --git a/api/soap/mc_api.php b/api/soap/mc_api.php
index f03ec526a9..76089d197d 100644
--- a/api/soap/mc_api.php
+++ b/api/soap/mc_api.php
@@ -208,11 +208,13 @@ static function objectToArray( $p_object, $p_recursive = false ) {
 	}
 
 	/**
-	 * Convert a timestamp to a soap DateTime variable
-	 * @param integer $p_value Integer value to return as date time string.
-	 * @return datetime in expected API format.
+	 * Convert a timestamp to a soap DateTime variable or ISO-8601 date.
+	 *
+	 * @param int $p_value Unix Timestamp.
+	 *
+	 * @return SoapVar|string datetime in expected API format.
 	 */
-	static function datetime($p_value ) {
+	static function datetime( $p_value ) {
 		$t_string_value = self::datetimeString( $p_value );
 
 		if( ApiObjectFactory::$soap ) {
@@ -223,16 +225,27 @@ static function datetime($p_value ) {
 	}
 
 	/**
-	 * Convert a timestamp to a DateTime string
-	 * @param integer $p_timestamp Integer value to format as date time string.
-	 * @return string for provided timestamp
+	 * Convert a timestamp to an ISO-8601 formatted DateTime string.
+	 *
+	 * @param int|null $p_timestamp Unix timestamp.
+	 *
+	 * @return string|null Formatted datetime.
 	 */
-	static function datetimeString($p_timestamp ) {
-		if( $p_timestamp == null || date_is_null( $p_timestamp ) ) {
-			return null;
-		}
+	static function datetimeString( $p_timestamp ) {
+		return date_timestamp_to_iso8601( $p_timestamp );
+	}
 
-		return date( 'c', (int)$p_timestamp );
+	/**
+	 * Converts a datetime string to a Unix timestamp.
+	 *
+	 * @param string $p_date_string Date string.
+	 *
+	 * @return int|null Unix timestamp, null when $p_date_string is blank.
+	 *
+	 * @throws ClientException When given string cannot be converted to Date.
+	 */
+	static function dateStringToTimestamp( $p_date_string ): ?int {
+		return date_string_to_timestamp( $p_date_string );
 	}
 
 	/**
diff --git a/core/commands/VersionAddCommand.php b/core/commands/VersionAddCommand.php
index fc81254322..ee9bd9c022 100644
--- a/core/commands/VersionAddCommand.php
+++ b/core/commands/VersionAddCommand.php
@@ -80,10 +80,8 @@ function validate() {
 				array( 'name' ) );
 		}
 
-		$t_timestamp = $this->payload( 'timestamp', '' );
-		$this->timestamp = is_blank( $t_timestamp )
-			? null
-			: ( is_int( $t_timestamp ) ? $t_timestamp : strtotime( $t_timestamp ) );
+		$t_date_string = $this->payload( 'timestamp', '' );
+		$this->timestamp = date_string_to_timestamp( $t_date_string );
 	}
 
 	/**
diff --git a/core/commands/VersionUpdateCommand.php b/core/commands/VersionUpdateCommand.php
index 64f20332f7..15dc8e13d8 100644
--- a/core/commands/VersionUpdateCommand.php
+++ b/core/commands/VersionUpdateCommand.php
@@ -153,12 +153,9 @@ protected function process() {
 			$t_version->obsolete = $t_obsolete;
 		}
 
-		$t_timestamp = $this->payload( 'timestamp' );
-		if( !is_blank( $t_timestamp ) ) {
-			if( !is_int( $t_timestamp ) ) {
-				$t_timestamp = strtotime( $t_timestamp );
-			}
-			$t_version->date_order = $t_timestamp;
+		$t_date_string = $this->payload( 'timestamp' );
+		if( !is_blank( $t_date_string ) ) {
+			$t_version->date_order = date_string_to_timestamp( $t_date_string );
 		}
 
 		version_update( $t_version );
diff --git a/core/date_api.php b/core/date_api.php
index 01b00fa318..b1bb7a9743 100644
--- a/core/date_api.php
+++ b/core/date_api.php
@@ -65,6 +65,54 @@ function date_get_null() {
 	return 1;
 }
 
+
+/**
+ * Converts a datetime string to a Unix timestamp.
+ *
+ * @param string $p_date_string Date string.
+ *
+ * @return int|null Unix timestamp, null when $p_date_string is blank.
+ *
+ * @throws ClientException When given string cannot be converted to Date.
+ */
+function date_string_to_timestamp( string $p_date_string ): ?int {
+	if( is_blank( $p_date_string ) ) {
+		return null;
+	}
+
+	# @TODO if we ever decide to require strict ISO-8601 date formatting in the
+	#       future, this should be enforced here.
+
+	try {
+		$t_dt = new DateTimeImmutable( $p_date_string );
+	}
+	catch( Exception $e ) {
+		throw new ClientException(
+			"Invalid date format '$p_date_string'",
+			ERROR_INVALID_DATE_FORMAT,
+			array( $p_date_string ),
+			$e
+		);
+	}
+	return $t_dt->getTimestamp();
+}
+
+/**
+ * Converts a timestamp to an ISO-8601 formatted date.
+ *
+ * @param int|null $p_timestamp Unix Timestamp.
+ *
+ * @return string|null ISO-8601 formatted date.
+ */
+function date_timestamp_to_iso8601( ?int $p_timestamp ): ?string {
+	if( $p_timestamp == null || date_is_null( $p_timestamp ) ) {
+		return null;
+	}
+
+	return date( 'c', (int)$p_timestamp );
+}
+
+
 /**
  * Gets Unix timestamp from a date string.
  *
@@ -87,21 +135,12 @@ function date_strtotime( $p_date_string ) {
 
 	$t_format = config_get( 'normal_date_format' );
 	$t_dt = DateTimeImmutable::createFromFormat( $t_format, $p_date_string );
-	if( $t_dt === false ) {
-		# date is not in expected format, try with default formats
-		try {
-			$t_dt = new DateTimeImmutable( $p_date_string );
-		}
-		catch( Exception $e ) {
-			throw new ClientException(
-				"Invalid date format '$p_date_string'",
-				ERROR_INVALID_DATE_FORMAT,
-				array( $p_date_string ),
-				$e
-			);
-		}
+	if( $t_dt !== false ) {
+		return $t_dt->getTimestamp();
 	}
-	return $t_dt->getTimestamp();
+
+	# date is not in expected format, try with default formats
+	return date_string_to_timestamp( $p_date_string );
 }
 
 /**
diff --git a/manage_proj_ver_update.php b/manage_proj_ver_update.php
index c5c86955c2..bbdd5b6a49 100644
--- a/manage_proj_ver_update.php
+++ b/manage_proj_ver_update.php
@@ -52,6 +52,7 @@
 
 $f_new_version	= trim( $f_new_version );
 $t_version = version_get( $f_version_id );
+$t_timestamp = date_strtotime( $f_date_order );
 
 $t_data = array(
 	'query' => array(
@@ -63,7 +64,7 @@
 		'description' => $f_description,
 		'released' => $f_released,
 		'obsolete' => $f_obsolete,
-		'timestamp' => date_strtotime( $f_date_order )
+		'timestamp' => date_timestamp_to_iso8601( $t_timestamp ),
 	)
 );