Our Koha partner libraries are all configured to pass koha-run-backups with the --days 2 parameter. Therefore, theoretically, any old backup files modified on a date two days ago will be deleted. However, since bug 30627 was pushed to 23.05.x and 23.11.x, we have noticed for our larger Koha instances (which run koha-run-backups for a long time each morning) the .tar.gz file from two days ago is often not deleted. This is because the .tar.gz file is not exactly 48+ hours old when the koha-run-backups runs the find command to identify old files to remove: https://github.com/Koha-Community/Koha/blob/286fc8e9833d55d694955849e4050d28a4b053a6/debian/scripts/koha-run-backups#L79 Often the .tar.gz file will be 47.9 hours old and therefore not deleted. The find command should switch to checking the modification date, to ensure all files created X days ago are deleted.
The -daystart option (from find's man) seems like a simple way to solve this by truncating the -mtime results IIUC.