maintenance subperiods "daily" and "weekly" have "every" field, which is not documented

it should be figured out how this works and fully documented.

a few scenarios to consider :

a) when exactly does "every" start - as in, when is the first invocation of the maintenance ?
b) if main period starts at 20:00 today but subperiod starts at 18:00 and ends at 19:00, when will "every" accounting start ?
c) if main period starts at 20:00 today but subperiod starts at 18:00 and ends at 21:00, when will "every" accounting start ?
d) if there are multiple maintenance subperiods that overlap or do not overlap, does that affect "every" in some way ?