It completely depends on your preferences and lifestyle. However, several hours early in the morning are considered golden hours, especially for the students. In the morning, the mind is very fresh, there is no disturbance in the environment, and a student can easily grasp the concept that they study. Many students also prefer studying late at night, and they do very well too. At last, it all boils down to when you are more comfortable studying with complete focus, energy, and stamina.