This bitmask specifies the starting day or days of the week on which a periodic time-range entry begins applying, with the same day potentially set in both the start and end day objects to represent a schedule spanning a full day. An admin sets bits for monday(2) through friday(6), for example, to have a business-hours policy start applying each of those weekdays. This object works together with timeRangePeriodicStartTime to pin down the exact moment recurrence begins on each selected day.