That is a simplistic understanding of how the process works
1) First of all, lets look at the processing issues. Any individual school will get roughly 5,000 individual applications for roughly 1,000 available interview slots. That means at least 80% of application at any individual school must be rejected pre-II, This in turn, makes medical school admissions for getting an interview a negative process to a large extent. That is, they look for reasons to not consider an application. Even if a school can easily discard half of the application it receives easily, that still leaves 2500 applications to distill to 1000 interview slots
2) When school has processing up to full speed which is not until after labor day at most places, at best they can fully evaluate and review a few hundred to several hundred applications a week. The rule of thumb is the roughly 12 weeks from Aug 15 until Nov 15 is when most of this is done with any indvidual application takeing 4 to 16 weeks or more. And it is not done in chronological order: High achievers, URM, family of alumni, feeder schools, associated UG programs, linked postbaccs, and other factor may push an app forward in the process. And with increase in the number of applications during covid, this balance has certainly gotten worse
3) Limiting factors are: a) the number of applications versus the time and resources available to process and b) the number of available interview slots. Since resources and time cant be expanded, the amount of time spent evaluating and reviewing an application will decrease as the cycle moves forward. Therefore, the later you are in the cycle, or the lower you are in the pile of applications to evaluate, the less time they have to fully evaluate and review and the "easier" it is for an evaluator or reviewer to reject. And remember if the more highly rated applications float up thru the pile earlier in the process as you go forward, evaluators and reviewers are dealing with lower rated applications as the cycle moves forward.
4) the concept of "on-time" does not really fit this process. Rather it is the potential impact or probability of how lateness can affect your chances. Very simply, as the cycle moves forward, the more applications pile up, the less time/resources can be devoted to an individual application and the higher potential risk to be more easily rejected from this processing.
So what is late? Yesterday was earlier than today and tommorrow is later. There is no way to have any solid info across schools, across application profile (ie how good your application is), and across any given cycle exactly when this curve suddenly goes down presenting a major risk due to lateness.
The rule of thumb is for all students at all schools, including highly selective ones, complete by Labor Day, meaning your application will have at least a good solid10 weeks for full evaluation is early/on time. That is, "lateness" will have no impact on your chances. For most "solid" applicants at most schools, mid-to-late September will be fine. After that however, you start this curve downward that could mean lateness will impact your chances. And this curve moves faster as the weaker you are as a candidate.
I will add two other things for the OP.
1) CARS is in fact the most difficult piece on the MCAT for most students to address, especially for running out of time. The only reason, I repeat the only reason that students run of time on the MCAT is because they do not know HOW to take which has absolutely nothing to do with content, knowledge or skill other than how to take the exam. If you do not have a practiced process of a disciplined time per section, per question, getting/guessing the best answer and moving on to the next section, then you are not taking the exam as it should.
2) No student should be retaking the MCAT in the same cycle unless it has been planned from the start. And even that I am really reconsidering