Revise prelim if relevant for subjects such as maths, go through all stuff covered in Term 4, and try to work ahead. Even if it doesn't make sense, it'll be just that one step ahead of the rest of your class when it comes to actually learning it, and you'll understand the concepts better.
Also, get your room/desk/study materials into order NOW, so it'll be easier when things start to get a bit hectic later on.
But apart from that, like pLuvia said, hours don't matter, it's what you DO in those hours that really counts.