Everyone is different so you have to use it in a way that is going to benefit you. If you smoke and find that you do worse on schoolwork, then I'd save it for after school or in the evenings. However, if smoking helps you to perform better, than you smoke when you're most comfortable. I know for me, even know, I can't smoke when I have alot of data to deal with....numbers, reports, spreadsheets, etc. If I just need to review or read something, then smoking actually helps me to focus more and come up with questions.