It depends on the school, but most secondaries come within 2-4 weeks of your having submitted the complete AMCAS application. The fact that your recommendation letters will not be in your hand until late july will have no bearing on when your secondary gets to you or when you can send it back. Most schools allow you to complete applications in steps - i.e. you can send in the secondary with the essays at one time, your recommendation letters later. The school just doesn't consider your secondary "complete" until they have everything in hand (AMCAS, secondary, rec letters, transcripts, MCATs, etc).