You need a solid understanding of the basic principles behind each subject, and you need to keep revising those principles. The fine details and memorization of facts can be studied effectively in the couple of months leading up to the exams, but you'll get nowhere if you don't understand what you're studying.
Dunno what others will say, but you can't put a figure on how much studying is required, except to say that it's ALOT. You need to live and beathe each subject, think about them constantly, and question yourself on everything, finding answers to those you're not 100% sure of.
I'd say that if you're not on a structured course you probably have to put in even more hours just because you're not immersed in it all every day.
I wouldn't give up your holidays unless they're very close to exam time. But definitely take your notes with you wherever you go.
hope that helps
abracadabra