The basic maintenance crons are scheduled @every 24h by default:
https://docs.gitea.io/en-us/config-cheat-sheet/#basic-cron-tasks---enabled-by-default

In practice, this means they will be triggered every 24h from the time that gitea has started.

I realize these default schedules can be overridden in app.ini (which I have done on my instance), but doesn't it make sense to schedule these at a fixed time with typically less user impact like @midnight?