Depends on the department/division, and depends on the manning level.What's the on duty/off duty schedule for the crew when a sub is at sea?
Reactor Controls Division was always undermanned on my sub.
We had two watch stations, Reactor Operator and Machinery 2. So, with 7 in the division, we had the chief who stood a supervisory watch, and then we had 3 section duty for both RO and AMR2.
3 section duty means, 6 hours on watch, 6 hours of (maintenance/recreation/casualty assistance team), and then 6 hours of sleep.
But, we often didn't have 3 qualified ROs. So, that means 2 section duty. 6 hours on, 6 hours off.
Except, when you're off, you're not "off".
Most of the RC div maintenance can only be done by a qualified RO. So, if you only have two RO qualified... one is on watch, one is doing maintenance. And you sleep when you can.
Then, when you throw in drills and emergencies...