I will be quoting descriptions of maintenance periods that can be legally created with current trunk in Configuration->Maintenances->Periods.

1. Let's start with this one:

   Period type	Schedule
   Daily	At 12:00 on every day

   Sounds awkward, I think that "on" shouldn't be there.

2. Let's continue:

   Period type	Schedule
   Weekly	At 12:00 on every Monday of every week

   First "every" implies that one can have two or more Mondays per week.

3. Now let's see some really weird stuff:

   Period type	Schedule
   Daily	At 12:00 on every 2 days
   Weekly	At 12:00 on every Monday of every 3 weeks
   Monthly	At 12:00 on day 1 of every January

   This does not sound like daily, weekly and monthly. In my opinion descriptions are good enough to not display confusing Period type at all. For configuration purposes they can be called "day/week/month based".

4. Minor compared to previous point:

   Period type	Schedule
   Monthly	At 12:00 on First Monday, Friday of every March

   "First" shouldn't be capitalized.

5. Last one:

   Period type	Schedule
   One time only	2017-11-07 00:00

   Seems that all translation strings are in place to produce date description with localized month name. But this may be inconsistent with the rest of interface.