Minor changes to `user_daily_visits` (#10324)

* Use fake time in tests in _get_start_of_day.

* Change the inequality of last_seen in user_daily_visits

Co-authored-by: Erik Johnston <erik@matrix.org>

changelog.d/10324.misc

@@ -0,0 +1 @@
+Minor change to the code that populates `user_daily_visits`.

synapse/storage/databases/main/metrics.py

@@ -320,7 +320,7 @@ class ServerMetricsStore(EventPushActionsWorkerStore, SQLBaseStore):
         """
         Returns millisecond unixtime for start of UTC day.
         """
-        now = time.gmtime()
+        now = time.gmtime(self._clock.time())
         today_start = calendar.timegm((now.tm_year, now.tm_mon, now.tm_mday, 0, 0, 0))
         return today_start * 1000
 
@@ -352,7 +352,7 @@ class ServerMetricsStore(EventPushActionsWorkerStore, SQLBaseStore):
                     ) udv
                     ON u.user_id = udv.user_id AND u.device_id=udv.device_id
                     INNER JOIN users ON users.name=u.user_id
-                    WHERE last_seen > ? AND last_seen <= ?
+                    WHERE ? <= last_seen AND last_seen < ?
                     AND udv.timestamp IS NULL AND users.is_guest=0
                     AND users.appservice_id IS NULL
                     GROUP BY u.user_id, u.device_id