At my school you're not allowed to go home until your last lesson of the day
But I don't care and I go home all the time in my double free's. I live 15 minutes walk from my house so I'd rather go home and work during the run-up to exams rather than stay at school and get distracted by my friends who are socialising in the common room. The school are quite mad at me going home and I've had quite a few letters, phone calls and talks. But I tell them straight, I'm not going to get enough work done staying at school. Once you send off your UCAS application, the school are pretty much powerless. They wouldn't dare to change your reference or punish you. As long as you stay on track academically, they don't do anything except the countless letters, phone calls and talks.
I wouldn't advise skipping any school time until you send off your UCAS application though.......