diff --git a/homeassistant/helpers/event.py b/homeassistant/helpers/event.py
index e615a6422f0..daad994bbd4 100644
--- a/homeassistant/helpers/event.py
+++ b/homeassistant/helpers/event.py
@@ -68,6 +68,10 @@ _ENTITIES_LISTENER = "entities"
 
 _LOGGER = logging.getLogger(__name__)
 
+# Used to spread async_track_utc_time_change listeners and DataUpdateCoordinator
+# refresh cycles between RANDOM_MICROSECOND_MIN..RANDOM_MICROSECOND_MAX.
+# The values have been determined experimentally in production testing, background
+# in PR https://github.com/home-assistant/core/pull/82233
 RANDOM_MICROSECOND_MIN = 50000
 RANDOM_MICROSECOND_MAX = 500000
 
@@ -1640,7 +1644,7 @@ def async_track_utc_time_change(
     matching_seconds = dt_util.parse_time_expression(second, 0, 59)
     matching_minutes = dt_util.parse_time_expression(minute, 0, 59)
     matching_hours = dt_util.parse_time_expression(hour, 0, 23)
-    # Avoid aligning all time trackers to the same second
+    # Avoid aligning all time trackers to the same fraction of a second
     # since it can create a thundering herd problem
     # https://github.com/home-assistant/core/issues/82231
     microsecond = randint(RANDOM_MICROSECOND_MIN, RANDOM_MICROSECOND_MAX)
diff --git a/tests/common.py b/tests/common.py
index 0b63a9a2ef6..6ee38b72532 100644
--- a/tests/common.py
+++ b/tests/common.py
@@ -59,6 +59,7 @@ from homeassistant.helpers import (
     entity,
     entity_platform,
     entity_registry as er,
+    event,
     intent,
     issue_registry as ir,
     recorder as recorder_helper,
@@ -397,9 +398,10 @@ def async_fire_time_changed(
 ) -> None:
     """Fire a time changed event.
 
-    This function will add up to 0.5 seconds to the time to ensure that
-    it accounts for the accidental synchronization avoidance code in repeating
-    listeners.
+    If called within the first 500  ms of a second, time will be bumped to exactly
+    500 ms to match the async_track_utc_time_change event listeners and
+    DataUpdateCoordinator which spreads all updates between 0.05..0.50.
+    Background in PR https://github.com/home-assistant/core/pull/82233
 
     As asyncio is cooperative, we can't guarantee that the event loop will
     run an event at the exact time we want. If you need to fire time changed
@@ -410,12 +412,12 @@ def async_fire_time_changed(
     else:
         utc_datetime = dt_util.as_utc(datetime_)
 
-    if utc_datetime.microsecond < 500000:
+    if utc_datetime.microsecond < event.RANDOM_MICROSECOND_MAX:
         # Allow up to 500000 microseconds to be added to the time
         # to handle update_coordinator's and
         # async_track_time_interval's
         # staggering to avoid thundering herd.
-        utc_datetime = utc_datetime.replace(microsecond=500000)
+        utc_datetime = utc_datetime.replace(microsecond=event.RANDOM_MICROSECOND_MAX)
 
     _async_fire_time_changed(hass, utc_datetime, fire_all)