Since Buoyancy is one of the first basic tasks that you need to learn in diving it would be a good idea to have it under control before the advanced class. It wouldn’t be fair to the other students in the class to have an instructor distracted by divers that don’t have their buoyancy tuned in. This would not only be a safety issue for you and the instructor but the other students. The advanced class is going to have you doing more advanced tasks that require more attention thus you need to have a few other things be second nature where you make the needed adjustments without thinking about it but.