I generally believe most movies should be shorter and that there’s a lot of room for addition by subtraction. That said, if a movie earns its runtime then I don’t think there’s an upper limit to how long it can be. Lawrence of Arabia is 3 hours and 45 minutes and it’s incredible, I don’t think I’d cut anything in it besides the long black intro screen which is a relic of its time. I would say justifying that run time gets exponentially harder past a certain point.
With Way of Water sitting at 3 hours and 12 minutes I do think Avatar 3 needs an intermission if it’s going to be longer. Asking people to sit and be fully engaged for 3 and a half hours is a big ask and having a chance to go to the bathroom, get snacks, stretch your legs, etc is needed for something that massive
I would say meditation could be helpful. Being present in the moment instead of looking forward prevents that creeping dread. Likewise planning things you want to do like hanging out with friends, going to shows/movies, and group activities will probably have you focused on those on those instead of starting your week