I feel like this is very subjective (obviously) I cannot comment on med school studying as I am not there yet. However, during my undergraduate I would tend to study a little bit each day instead of pulling all nighters cramming (cramming = very inefficient for me but works for some). This way by the time exam time came around I would just chill and look at my notes peacefully knowing that I already knew the info. This would yield much more time spent hanging with friends, girlfriends (break ups), cycling and mountain biking, and going out to bars/clubs during the weekend. I feel like self discipline is the best. Some semesters were often more rushed than others. Biochem combined with physics was pretty rough as I often tended to overstudy as you can always practice more with physics. I hope I can acclimatize well in medical school with the rigor and my tendency to perfect.
For now, especially with MCAT. I average around 7 hours of studying. I just can't grasp how some study 12+ hours. I usually get through a TBR chapter, finish 1001 problems and do 4 practice passages and cap out at 5-6 hours.