It depends... some people are good at studying at night and some prefer to study in the morning before lunch. I am the type of person whose brain is most active half of the day. And after lunch time, I am not that much active...and at night I get so dizzy while studying. But that doesn't mean i don't study. So what you should is determine the time of the day you are active to study. Use that time to study more. And then for the time of the day you don't feel well to study, don't pressure yourself to study too much. Take small breaks and use videos rather than deep reading.....