I have the ENTIRE summer: SAT/ACT Prep?

Think about it. It's summer. Are you really going to want to study for 7+ hours a day? I HIGHLY doubt it. I say, study at least an hour a day (really study!) everyday and you should be fine. When it comes closer to the test date, bump it up an hour for studying. You don't need to study for a third of the day, it's summer. RELAX!