hey there! Honestly i had the same problem when I was in yr 12 ( i am currently yr 13 now). I would say that you should try and rest for 30 mins to 1 hour and then start studying as soon as possible, so that you can finish early and then do all the other things you want to do. personally i hate studying too late at night cuz i am just too tired to focus. try to make a plan and stick with it, it will really help you if you stay committed to it. also i don't know how your sixth form works but in my one we have 'independant study sessions' during the day, which is really helpful cuz you can just do most of your work then and basically be free at home. you could also try and get ahead of everyone else during the weekend/holidays by preparing for future lessons, so that you already understand the topic/ have a decent understanding of it so that when you get to it in class, you don't have to go over it again at home.