It depends on what schools you're looking at. There are some schools without rolling admissions where a late application won't hurt you too much. Also, you could probably get away with a late application to some in-state schools. However, a late MCAT will hurt you at a large number of schools (ie the schools that don't fall into the above two categories). Still, the importance right now is getting a good MCAT. Focus on that first. You can always reapply early with a good MCAT. Yet, it doesn't matter when you apply if your MCAT isn't good.