In 15 months I've been held out twice for 18 days. I would say the average is about 12. This is of course dependent on your bidding. The 7/7 schedules seem to get used less. I choose the bids with 18/12 because even though 18 is long (or the possibility of 18), having 12 off in a row feels like a vacation. And some of the bids are 12/12/6 or 11/12/7. There are varying schedules but they all have some combination of 18 on and 12 off.