This BITS object sets the starting day or days of the week on which a periodic entry's referenced configuration begins taking effect, combined with timeRangePeriodicStartTime to form the full start day-and-time; the same day set here must also be set in timeRangePeriodicEndDay if multiple days are specified. An admin uses this to define exactly which weekday(s) a recurring schedule window opens on. For example, an admin might set both the monday(2) and friday(6) bits to mark those as the days the schedule window starts.