Someone asked me this years ago and I've discussed it with people ever since. If you HAD to work 100 hours every week, but could choose your own hours/days would you do?
7x 14 hour shifts?
6x 16 hour shifts?
5x 20 hour shifts? (!)
To ensure as much of a balance as possible, I would probably choose to work 5x 16 hour shifts during the week, say 7am-11pm, with 10 hours on Sat 8am-6pm and Sunday midday-10pm, giving me an evening and whole morning off on the weekend.