diff --git a/cobald_hep_plugins/timer.py b/cobald_hep_plugins/timer.py
new file mode 100644
index 0000000..25bd37c
--- /dev/null
+++ b/cobald_hep_plugins/timer.py
@@ -0,0 +1,92 @@
+"""Time-based demand control decorators and helpers."""
+
+from __future__ import annotations
+
+import asyncio
+from datetime import datetime, time as datetime_time
+from typing import Mapping, Union, Iterable
+
+from cobald.daemon import service
+from cobald.interfaces import Pool, PoolDecorator
+
+TimeInput = Union[str, datetime_time]
+Schedule = Mapping[TimeInput, float]
+
+
+def str_to_time(value: str) -> datetime_time:
+    """Convert a HH:MM string into a :class:`datetime.time` object."""
+    try:
+        hours_str, minutes_str = value.strip().split(":", 1)
+        hours, minutes = int(hours_str), int(minutes_str)
+    except ValueError as exc:
+        raise ValueError(f"invalid time specification {value}")
+    return datetime_time(hour=hours, minute=minutes)
+
+
+def latest_timestamp(
+    times: Iterable[datetime_time],
+    *,
+    reference: datetime_time | None = None, # easier to test with
+) -> datetime_time:
+    """Return the latest timestamp with respect to the current time."""
+    ordered_times = sorted(times) # ascending
+    current_time = datetime.now().time() if reference is None else reference
+    for candidate in reversed(ordered_times): # descending
+        if candidate <= current_time:
+            return candidate
+    # All configured times are in the future relative to ``current_time``.
+    # return latest timestamp
+    return ordered_times[-1]
+
+
+@service(flavour=asyncio)
+class Timer(PoolDecorator):
+    """
+    Decorator that adjusts demand based on a daily schedule.
+
+    :param target: pool being decorated
+    :param schedule: mapping of ``HH:MM`` times
+                     to the demand that should become active at that time
+    :param interval: interval in seconds between schedule checks
+    """
+
+    def __init__(
+        self,
+        target: Pool,
+        schedule: Schedule,
+        interval: int = 300,
+    ):
+        super().__init__(target)
+
+        assert interval > 0, "Interval must be a positive integer."
+        self.interval = interval
+
+        schedule = {str_to_time(key): value for key,value in schedule.items()}
+        self.schedule = schedule
+        self.latest_sched_demand = self._refresh_demand()
+
+    @property
+    def demand(self) -> float:
+        return self.target.demand
+
+    @demand.setter
+    def demand(self, value: float) -> None:
+        # Ignore user supplied demand and always enforce the scheduled value.
+        self.target.demand = self.latest_sched_demand
+
+    async def run(self) -> None:
+        """Update the demand periodically according to the schedule."""
+        while True:
+            self._refresh_demand()
+            await asyncio.sleep(self.interval)
+
+    def _refresh_demand(self) -> float:
+        """Look up the demand that should currently be active."""
+        latest_sched_time = latest_timestamp(self.schedule.keys())
+        self.latest_sched_demand = self.schedule[latest_sched_time]
+        self.target.demand = self.latest_sched_demand
+
+        assert self.latest_sched_demand >= 0.0
+        assert self.target.demand >= 0.0
+        
+        return self.latest_sched_demand
diff --git a/docs/index.rst b/docs/index.rst
index f243cc8..7a55197 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -27,6 +27,7 @@ HEP Plugins for COBalD/TARDIS
    :caption: Available Plugins
    :hidden:
 
+   plugins/timer
    plugins/stopper
    plugins/example
 
diff --git a/docs/plugins/timer.rst b/docs/plugins/timer.rst
new file mode 100644
index 0000000..f126a0c
--- /dev/null
+++ b/docs/plugins/timer.rst
@@ -0,0 +1,66 @@
+#############
+Timer Plugin
+#############
+
+.. py:module:: cobald_hep_plugins.timer
+    :synopsis: Time-of-day demand controller
+
+The :class:`~cobald_hep_plugins.timer.Timer` plugin enforces a recurring,
+time-of-day schedule for the demand of a target pool.
+
+At its core the Timer plugin stores an ordered mapping of ``HH:MM`` to demand values. Whenever the demand is updated,
+``Timer`` looks for the latest schedule entry that is not later than the current
+time and applies the demand from that entplugin pool. If the current
+time is earlier than the first entry, the scheduled value from the previous day
+becomes active. User supplied values to :attr:`demand` are ignored so that the
+scheduled demand is always in effect.
+
+Configuration
+=============
+
+The class accepts three arguments:
+
+``target``
+    The pool whose demand should follow the schedule. This is the same target
+    you would normally use in a COBalD pipeline.
+
+``schedule``
+    A mapping where the key is either ``HH:MM`` and the
+    value is a floating point demand. The schedule must at least contain one
+    entry and demand values must be non-negative.
+
+``interval`` (optional)
+    Number of seconds between two schedule checks. Defaults to ``300`` seconds.
+
+Schedule semantics
+==================
+
+Demands remain active until the next configured timestamp is reached. For
+example with the fragment below.
+
+.. code:: yaml
+
+    schedule:
+      '08:00': 50   # from 08:00 until 12:30
+      '12:30': 120  # from 12:30 until 20:15
+      '20:15': 10   # from 20:15 until 08:00 next day
+
+
+Example configuration
+=====================
+
+An example snippet for the YAML interface in a COBalD configuration file:
+
+.. code:: yaml
+
+    - !Timer
+      target: SomePool
+      schedule:
+        '06:00': 20
+        '09:00': 80
+        '17:30': 10
+      interval: 120
+
+With the configuration above the decorator wakes up every two minutes, updates
+``target`` with the most recent demand of the schedule and thus enforces a
+repeatable daily pattern.
diff --git a/pyproject.toml b/pyproject.toml
index 085edff..c928796 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -52,6 +52,7 @@ Source = "https://github.com/MatterMiners/cobald-hep-plugins"
 # v name used in YAML v    v --- package/module --- v v class/function
 CobaldHepProjectExample = "cobald_hep_plugins.example:DemandScale"
 Stopper = "cobald_hep_plugins.stopper:Stopper"
+Timer = "cobald_hep_plugins.timer:Timer"
 
 [tool.flit.module]
 name = "cobald_hep_plugins"
diff --git a/tests/test_timer.py b/tests/test_timer.py
new file mode 100644
index 0000000..042a509
--- /dev/null
+++ b/tests/test_timer.py
@@ -0,0 +1,80 @@
+from cobald_hep_plugins.timer import Timer, latest_timestamp, str_to_time
+import pytest
+import datetime
+from datetime import time as datetime_time
+from .utility import MockPool
+
+SCHEDULE = {
+    "18:03": 30.0,
+    "06:59": 10.0,
+    "00:30": 0.0,
+    "12:38": 20.0,
+}
+SCHEDULE_DATETIME = {
+    datetime_time(18, 3): 30.0,
+    datetime_time(6, 59): 10.0,
+    datetime_time(0, 30): 0.0,
+    datetime_time(12, 38): 20.0,
+}
+
+
+def test_str_to_time():
+    for str_time, expected_time in zip(SCHEDULE.keys(), SCHEDULE_DATETIME.keys()):
+        assert str_to_time(str_time) == expected_time
+    with pytest.raises(ValueError):
+        str_to_time("invalid")
+    with pytest.raises(ValueError):
+        str_to_time("25:00")
+    with pytest.raises(ValueError):
+        str_to_time("12:60")
+
+def test_schedule():    
+    timer = Timer(target=MockPool, schedule=SCHEDULE)
+    expected = {
+        datetime_time(18, 3): 30.0,
+        datetime_time(6, 59): 10.0,
+        datetime_time(0, 30): 0.0,
+        datetime_time(12, 38): 20.0,
+    } 
+    assert timer.schedule == expected
+    
+
+@pytest.mark.parametrize(
+    "reference, expected_latest",
+    [
+        (datetime_time(18, 2),  datetime_time(12, 38)),
+        (datetime_time(18, 3),  datetime_time(18, 3)),
+        (datetime_time(18, 4),  datetime_time(18, 3)),
+        (datetime_time(0, 0),   datetime_time(18, 3)),
+        (datetime_time(23, 59), datetime_time(18, 3)),
+        (datetime_time(7, 0),   datetime_time(6, 59)),
+        (datetime_time(12, 1),  datetime_time(6, 59)),
+    ],
+)
+def test_latest_timestamp(reference, expected_latest):
+    latest = latest_timestamp(times=SCHEDULE_DATETIME.keys(), reference=reference)
+    assert latest == expected_latest 
+
+def test_demand():
+    timer = Timer(target=MockPool, schedule=SCHEDULE)
+    for demand in     [
+        15.0,
+        25.0,
+        5.0,
+        0.0,
+        30.0,
+    ]:  
+        
+        # set demand directly
+        timer.latest_sched_demand = demand
+        # ignore demand setter
+        timer.demand = demand + 2.
+        assert timer.demand == demand
+
+def test_non_negative_demand():
+    schedule = {
+        "10:00": -5.0,
+    }
+    with pytest.raises(AssertionError):
+        timer = Timer(target=MockPool, schedule=schedule)
+