My sleep schedule is a nightmare and has been for the past 5 years due to the fact that I work third shift only twice each week.
I actually sleep 8 hours at a time, 6 times each week. The seventh time I lay down is the morning after my two 3rd shifts, and that is just a 2 or 3 hour nap. Then I am back on a first shift schedule for the next 5 days. Then I stay up for about 20 hour straight on Sunday and switch back to third shift again.
So I guess if you figure 7 nights at 8 hours a night would be 56 hours of sleep. I'm only sleeping 6x8 = 48 plus the nap which gives a total of 50 or 51 hours. But, I feel it.