Dear client It's nice that you want to maintain balance between sedentary activities and exercise. It is advisable to take breaks after 45 minutes of studies. You can plan your  routine in slots of 1hour and can fix sets of workouts in between. If you visit gym then keep it after mental fatigue is evident. Gym followed by a wash will refresh you .if you do jogging or swimming etc.then preferably in morning hours so the sunlight exposure will keep your body clock in order.

I believe you should discuss your concerns in detail with a mental health professional to gain an insight about nature of problem and ways to overcome it through psychotheraputic techniques Consult with me or any psychologist for therapy and counseling Connect with me through practo Follow my Facebook page "juhi parashar -psychotherapist " for mental health issues All the best Seek help for early recovery

It depends upon your schedule. You study late night or start studying during wee hours. Suppose you start your day at 4am after studying for 2hr. you can go to gym around 6am or if you start your day around 10am because of late night study then it's better to go to gym during evening hours. It's good that you along with studies you r sparing your time for exercise also which is essential and will always kerp your moral high. Study well goodluck for future.