I would recommend both! Try to study in 75 or 100 minute chunks followed by 6 minute breaks where you use the restroom, quickly eat something (prepare whatever you will eat on test day before you start studying and consume this), then force yourself to jump back into DEEP studying. This regiment, coupled with timed practice tests will really increase your indurance. Just make sure to give your mind a break after studying, and totally take evenings off after a long day of studying. Also, go VERY LIGHT on the day before your test. You want your brain to be functioning. Also, I would recommend planning a nice dinner or some cool event with friends or family the night after your test. This will give you something to look forward to regardless of how you do on your test. A lot of times that "light at the end of the tunnel" can really help motivation and endurance. Good luck to you!