Hi sfildes,
4 hours sounds like a lot of time. A root canal treatment is like a loooonger and a bit more boring filling. You mentioned people acting like it is bad - would you mind sharing what exactly you mean by "bad"? I know some stories about root canals being painful, that comes from many many years ago when dentists weren't that good with numbing and people weren't good with asking to be numbed up more. Nowadays this is not a problem anymore. When it comes to your jaw, there is a thing called a biting block (we called it "tooth pillow" which I find nicer to be hones), it's simply a small piece of rubber that gets placed on the side that is not worked on and you bite on it. Biting on something is much easier and more relaxing for your jaw than keeping it open so just ask your dentist to try that out to see whether it helps.
If you feel 4 hours is too long, maybe asking to do the procedure in two visits may be a good idea. I see how for the dentist doing them both is more convenient, but you are the customer so if you would feel better with one at a time, that may be an option too, particularly if there is no sedaiton involved.
All the best wishes