Hey Rob,
Optimal time is between 1 hour and 4 hours per day, with diminishing returns toward the higher end of that. If you only do 1 hour per day, I think it’s important to do them back to back because there’s a cumulative effect. I’ve never hung 4 hours per day, but I have gotten up to 2 hours per day before. I imagine you still want to do at least a few back to back in each session. So for example, 4 sessions of 1 hour hang time (plus breaks) each would be fine. But breaking it up in to 12 separate sets with 1 hour rest between each set would be less beneficial. Some people think doing 2 sessions per day is better than all at once. Other people prefer all at once. It’s personal preference.
Each time you hang your first set of the day, it squeezes out the extracellular fluid beneath the hanger, but tightening down for that first set of the day is always more difficult than the subsequent sets. If you wait an hour between sets, that fluid matrix comes back and you’ll never get properly tightened, and it’s just less comfortable in general. So at least do sessions of 3 sets (1 hour in hanger) each.
It probably goes without saying, but work your way up gradually over a period of months if you’re going to hang that much time. Good luck!