Is it better to wake up early or stay up late to study?

The most important thing is that you are getting enough sleep for your brain and body to recharge fully, or at least as much as it possibly can. You know better than anyone whether you are a morning person or a night owl, so try to set a schedule that best suits your natural rhythm. When deadlines are imminent and you don’t have this luxury, it is typically better to stay up and work late the night before rather than wake up early to get it done right before a test—if there is more work than you anticipated, you have a greater buffer to get everything done (and done well).