Well it wouldn't hurt to start studying early but it will be more beneficent if you really focus and understand the concepts in your orgo and especially physics classes.
So like, you probably don't know about centripetal acceleration, virtual images, or electric circuits. If you really focus on them during your classes, once you finish the class and start to prepare for MCAT, you will be able to recall the material much easier.
Don't take the classes just for the grade. Really understand it in detail and your hard work will show your grade anyway.