First we have to take a step back and evaluate what kind of person we are: a dayhawk or a nightowl? Taking this into account will help you realize the energy and enthusiasm you put forth when it comes time to retain information. Once this is clarified, we give you some pros and some cons for each.
Studying during the day
The day also has its obstacles
Studying at nighttime
The night also has its inconveniences:
Taking into consideration all of these points we are sure you will be able to find the best hours of study suited to your needs.