Half of my exams are in the afternoon, starting at 12:20pm. The good thing is I can allow myself at maximum two extra hours of sleep so you wake up feeling refreshed and not dead inside. I think you should wake up at a reasonable time maybe 10 or earlier depending in your transport and circumstances, then either do some light studying at home or come to school early and study with the rest of your cohort/friends in your school library. We can all panic together!!!