I have heard lots of opinions about the earlier you apply, the better.
I agree with that: the earlier the better.
Some indicated that everything should be out by end of July,
End of July isn't early. That's 2-3 months into the cycle. You might
get away with applying at the end of July.
Apply as close to the open date as you can. The open date for MD is June 1, for Texas it's May 1. DO is also in June but early is less interesting for DO (also, DO deposits are HUGE and you lose your deposit if you take another acceptance).
Note that I'm talking about "early" not about "possible". You can always find an anecdote of somebody applying stupid late and getting in anyway. It's foolish to use detail-free anecdotes to make your plan.
leaving things till Sep is a bad bad idea...
Waiting until September looks like you didn't plan. Or you're apathetic.
But you have to do what you have to do.
If you have an insane app with ridiculously high numbers, and you are a mature and compelling applicant who is delightful to review and interview, then an early app isn't an edge you need.
If you're closer to ordinary, or you have some deficiencies, then you need every advantage you can get.
Usually MCAT scheduling is what folks get hung up on. If you take the MCAT after April, you don't get your score until after June. Imho, if your MCAT schedule has you ready for the test after April, or your April test doesn't go well, then I suggest you need to think really hard about taking another year to get ready to apply. Applying is extremely expensive and emotionally excruciating - try to just do it once. In June.
Best of luck to you.