Ideally you would take your test in April or earlier because you'd get your score back in May (or earlier) and it would help you in selecting competitive schools to apply to. You'd simply have more information. However, the world is not always ideal.
You can take it in May and choose where to apply this cycle based on your practice scores, overall competitiveness, and mission alignment. You can also apply before you get your score back and thus be "early" in the cycle. You can then add schools if based on your actual MCAT score you feel you aimed a little high or low. That's one approach. Another approach, is to initially apply to your in-state schools or one or two of your top choices so that your app is verified by AMCAS as soon as it gets the score, and then you choose additional programs to apply to with knowledge of your score, but your app is already verified.
That's the long answer. The short answer, is you don't need to postpone your application because you received your score in May.