Mmm... This is a tricky question...
I think it's a matter of knowing your priorities & time management. My hobbies are watching anime, series, drawing, and playing games.
I think what worked for me best when I was a student was to watch anime/ series that are not completed yet, meaning I have to wait each week/s for the next episode/s. This helped me a lot in controlling myself not to binge-watch. I just do this when it's my vacation or I don't have anything due. As for games, this was really hard for me to control. I think what I did was I listen and focus during classes so that I don't need to study a lot during exams (for subjects that were easy), but I make sure I give enough time to study for classes that were harder. I reward myself after with playing games hard-core. And while I study, I try to watch something every now and then to not stress too much.
I don't have much time doing sports/ exercise (well... because I'm too lazy for it) but I try to walk a lot to make up for being a couch potato. Sometimes, if I'm really motivated, I do some aerobics at home in the morning.
I think it's simply discipline.