I have an RDS instance with a backup window of 22:00-22:30 UTC and a retention period of 35 days.

I have noticed several peculiarities:

• There are 55 automatic backups currently stored, not 35 as I would expect. 20 of the days seem to have 2 snapshots rather than 1.
• 19 of those 55 snapshots have start times outside the backup window. If they were a couple of minutes outside I could cut AWS some slack, but these times are all over the place.

17/05/2024 03:01:05
17/05/2024 11:26:10
17/05/2024 14:35:32
20/05/2024 12:36:04
21/05/2024 15:40:30
23/05/2024 17:06:00
24/05/2024 23:05:21
27/05/2024 22:45:26
28/05/2024 09:05:34
29/05/2024 17:50:23
01/06/2024 16:00:29
04/06/2024 12:50:47
06/06/2024 04:40:31
06/06/2024 05:30:47
08/06/2024 07:05:29
08/06/2024 16:40:31
08/06/2024 18:30:40
12/06/2024 16:35:40
17/06/2024 09:11:00

This is a problem because snapshots that start outside the backup window have been interfering with SQL Server native backups that start at other times of day. I really need all snapshots to start within the backup window. Is there any way I can achieve that?