It sounds like a variation on a six-hour shift system. Any seagoing vessel with a crew complement of 2 or more sailors is going to try to have one portion of the crew at work at all times. Skimming [1] I didn't see a 6-on/6-off system, but I believe, the skipper has the last word even when asleep.
Yeah why anything? Many of the policies on the boat seemed solely to punish the employee. Some boats had it 12 x 12, some boats even had 4 x 8 x 4 x 8, which is just a normal 8 hour day. But not my boat.
I lasted less than a year, it was also hell to me.
[1] https://en.wikipedia.org/wiki/Watchkeeping#Six_Hour_Shift