i cant emphatically concur strongly enough. When I get the slew of questions of “how late is late for MCAT, application, etc” or “can I take 3 prereqs AND prep/take MCAT AND fill out AMCAS AND take 4 weeks out of the country” or whatever the question is, it makes me want to tear my hair out!
An applicant is fully, completely, totally in control as to WHEN they submit an application is submitted. Nobody is holding a gun to your head saying “submit now or I will blow your brains out.” If something comes up to delay, you CHOOSE whether to submit or not. Your choice, no one else
As for planning ahead, as far as I am concerned applicants should concerned what is the most optimal timing and path to apply not when is the latest. On that note, I suggest that applicants need to have their MCAT score (and all prereqs) done no later than January of application year. With MCAT score and GPA you can start targeting and researching schools, begin on their secondaries, and be fully ahead of the AMCAS submission.