Thanks for replying back guys. I'm doing a PhD in Psychology (Year one; so there's not much lab work, if at all). I usually study in the afternoon and evening, from 2 to 6 and then from 7 to 9. I rarely work at night (except in very busy period). I'm also trying to work in the morning, say on hour or so. But I usually save the morning to collect materials at the library. How many hours of study a day would you say are enough ? Thanks.