This enables customizing the time of day within which periodic refresh occurs.
Previously docs said it happens between 12am-4am which is misleading,
because the code effectively allowed refresh until 4:59:59 AM.
The default window is now '0-5', which is practically the same as before.
The comment about checking every 24h hours has been fixed as well.
This hasn't been true since commit c4fa76f217
Signed-off-by: Kamil Domański <kamil@domanski.co>
04b1103778