The official deadlines vary from school-to-school but I think most of them are somewhere around October 15th. However, the deadline means nothing...you want to submit as early as possible. If you're confident you will be applying this cycle you should submit now even if you're not taking the MCAT until August. If you want to wait I would still submit in August if you're getting decent scores on practice tests rather than wait for results in September.
I was in a similar position - I took my MCAT in August, waited for my results in September, submitted my primary ASAP, had my primary verified in October, and by the time I had received and submitted secondaries it was early November. So...there can be quite a bit of turn-around time. This turned out OK for me but many schools have already handed out most of their interview invitations and many of their acceptances by that time.
