"After about 36 hours the CO2 levels would be a lot higher, the O2 partial pressure would be a lot lower, and a couple of drill sets would have worn the edge off everyone. Sleeping wasn't much of a problem after that..."
I don't recall more than one or two days of not being able to sleep underway. Of course, being underway 300 days a year, port and starboard watch rotation, weekly ops when we had to come in at midnight for reactor startup, and stay til midnight on Friday for shutdown and maintainance may have had something to do with that. Of course, there's always the joy that is ORSE workup. Six hours on watch running drills, six hours after watch as part of the emergency response team, and six hours before watch to as part the team conducting drills.
I think that in my eight years in the Navy, I worked an average of 90 hours per week. Of course, on the boat, your manpower is limited not only by how many sailors you get, but how many racks you have for them.