For this sentence you would want to say: "I can study at the university at any time of the day" - which means: whether it's early in the morning, the afternoon, or 1am at night, you can go to the university to study. It is open 24/7

I suppose you meant to say that you can go inside the university building 24 hours a day in order to study, in which case, I would say: I can study inside the university anytime.