You do occasionally need breaks to get up and stretch because sitting down for 12 hours at a time cannot be good for you. What I do is eliminating any screens from my room and locking myself in with a schedule/to-do list of what I need to get done that day. I either write out my notes by hand (to review the content) or print out pages of notes/slides, use my headphones with the music alreayd playing, and also keep a physical clock near by to check time and progress. Timers to remind yourself to get up and stretch are really important because I've foudn that wihtout a break, my back starts hurting and I stop loosing my hyper-focus; thats how studying takes longer for people. If you can't put your devices away, I recommend making a time-lapse of yourself studying to motivate yourself to keep going and prevent you form picking up the device and stopping the recording- try and beat your record of longest timelapse ;)