I think its less about quantity and more about quality--obviously this doesnt mean studying for an hour a day, but if you set unrealistic goals and end up using your ten hours half studying and half being bored, pissed, or spacing out(like I would) then its not worth it. One persons five hours could be another persons 8, or even 10. Its really about figuring out what type of student you are, and how you learn best. For me at least, I went through all the practice tests, wrote down everything I missed, made notebooks of notes for each of the sciences, and then made a stack of material for orgo, chem, and bio, and read through each of them repeatedly for about a month.