Originally Posted by Tyrion

They won't drop the last or first day because they don't want you scheduled for 6 days in a row. If you start day 1 with 4 AM RAP (default schedule) they can't work you past 10PM on day 6. So their solution is to give you 4 on, 1 off, 2 on (or something similar). Bonus, since you now have a transition day off, they can extend you into an overnight and not give you a return day.