submit it as soon as u can. the MCAT results will go from the AAMC to the AMCAS automatically. don't worry about that. but getting it submitted early is crucial... and posting in the right forum is crucial too.
I was able to get mine on June 15th. I submitted my stuff just after I got the scores because I wanted to make sure my scores were acceptable and that I wouldn't need to check the box that says something along the lines of "I'll be taking the August MCAT". I don't think waiting until mid-June to submit will put you at a significant disadvantage, it's those people that wait until the day before the deadline that have problems.
yeah i prepared the AMCAS ready for submission, but waited till the MCAT results were out before submitting it. I wanted to make sure that the schools i was choosing matched the score i got and to give me a chance to add or remove schools. that said, i think you can add schools after submitting your AMCAS, but i don't think you can remove any.