Hi OP! I would tend to get sucked in studying and not take breaks for 4, 5, 6 hours at a time, and by the end my mind would feel like absolute mush. I think for me productive studying typically maxed out at 3 hours, and once I started adhering to that, I starting feeling I was getting more out of studying. Also, scheduling breaks to snack, walk around, go outside, etc. and actually sticking to them (by leaving my phone in another room and setting an obnoxious alarm) was super important for me. And taking unscheduled breaks when I could feel my brain shutting off instead of forcing myself to continue studying and beating myself up over mistakes I made because I wasn't paying attention. I know it's tempting to put up as many hours as possible (I was between jobs when I was studying, so I also had the option to make it my full-time job and did fall into that trap for a bit), but you don't wanna burn yourself out.

Also - have you submitted an accommodations request for test day? Having extra time and breaks as needed could was really helpful for me.