<p>You should really just start prepping now.
AP Bio is still a very content heavy course despite the course change in 2013. Unless you have a mighty memory, it will take you a great deal of time to remember all the information needed.
AP Chem and BC are both very concept and problem oriented course. If you are doing BC, I will presume you have already completed AB. If you feel you can easily grasp the concepts taught and be able solve the problems with ease, you will be fine.
If not, be prepared to invest in a equally great figure of time.</p>