The specific time to study can not be defined. One needs to find the right for themselves. Theories do exist on how one must divide their time and schedule their day for healthy stable education.
Different people have different preference regarding time to study. Some prefer to study early mornings, while some prefer to study at late night hours. On the other hand, some prefer studying in between the working hours of the day.
It is however advisable to have studies in early hours. At early hours, the concentration is at its peak. It helps to grab most of the topics more clearly and effectively.
I hope this answer helps!😊