Subjective for everybody depending on their knowledge, but generally I'd allot 4-6 weeks in advance for studying this. So OP, no, this is definitely not too early especially if it's for the August PCAT. You have like 3 weeks plus only!
If you have taken (summer) classes of calculus, orgo, biology, and/or anatomy and stuff like that, more power to you, because the stuff should still be fresh in your head and less studying would be required possibly.