LPT: When planning studying goals, base them off of work done rather than on time spent.

For example, your goal could be to study 2 hours at the library everyday but you could actually end up accomplishing half an hour's worth of work due to distractions, and whether or not you used your time effectively you feel accomplished when the time's up. Rather, set your goals in relation to your work (10 pages, 10 exercises), so no matter how much time passes you'll have a more concrete goal to reach and a more productive approach.