A lot of it depends on your conditioning as to your ability to work this way. It's done and it's done safely everyday. 4 hours on 4 hours off with at least 10 of these hours hours off being working hours. I'll explain. 7am report to work center. 8 am go on watch meaning operating machinery. 12 pm go off watch and back to work. 5-6pm stop work for day and eat shower ect 8-12 pm go on watch. Go to bed around 1 am get up at 6 am and start over. Do this for 6 months as do many of our United States Navy personel aboard ships especially the Snipes.
The Navy has done it ever since but the person has to be conditioned to the task. If you are accoustomed to this type work it becomes routine. BTW I was also an OTR truck driver at one time. True the driver may run up to 20 hours including stops to get to a destination or stopping point for sleep. He may as well likely stay there at least 24 hours waiting on another load to be scheduled. I was stuck in some places for nearly a week. Califorina was a truckers nightmare as far as that goes. If you didn't have a reefer you were going to sit a spell. In that time you don't earn a penny. You drive by the mile not by the hour. You don't move you don't get paid.
In general a weekend home every two weeks caught my aviable drive hours up if I was out of time.
Looks like you know all too well the madness that is a Navy schedule *s* My husband is an STS3(SS) aboard a fast attack sub. They now schedule 'mandatory sleep' periods for those on duty before they go to stand watch, and he says it makes a big difference (especially when he gets stuck with the midwatch again).