Rule One: Take A Breath
This question comes up every year and every year I say the same thing. It is mostly meaningless. While you are likely to get a secondary sooner, it is unlikely to have any impact on when you are evaluated, if you get an II, etc.
1) AMCAS transmit applications to school in batch format. That is all applications on that day are transmitted together is no particular order
2) schools will screen and prioritize for evaluation based on academics and other factors. It normally takes 4-16 weeks (1-4 months) to get evaluated and reviewed for II
3) therefore rarely are applications considered in chronological order
4) your evaluation will not begin until all parts of your application (primary, secondary, mcat, LOR) are received.
Fully agree - being in the first "batch" of applications transmitted is largely just something overblown in importance. Being verified and transmitted a few days after the "first batch" is not going to diminish your chances significantly. I can attest to the fact that schools don't even evaluate applications strictly in the order they were received.
The primary reason I made this and included that date of first transmission is to try to reassure people who are likely going to post on this forum terrified that they won't be able to submit first-day applications, especially this cycle.
I believe I've heard the general rule of thumb is to have all secondaries submitted by Labor Day. Assuming you want at least 2 weeks to finish your secondaries, that would make the latest time for you to be complete (primary-wise) and submitted would be the beginning of August.
With all due respect, you really should consider modifying #4 this year.
MCATs were cancelled from 3/27 through 5/21, resuming on 5/29 and continuing right through the very end of September. A significant number of schools have publicly stated that they WILL begin an evaluation without MCAT scores this year, as an accommodation to those impacted, understanding that scores might not be available until the end of October. It is misleading to state that nothing is going to happen until that time when some schools (see CA) will send secondaries and even IIs without them this year.
Frankly, I don't think this is really the case. What schools constitute as "evaluating" an application may mean simply deciding whether or not to send a secondary and then putting you on hold afterwards regardless of whether you complete the secondary until they get your score. Furthermore, getting a secondary is nothing to really be proud of - a significant number of schools will send secondaries to every person who submits a primary.
There's also other nuances to the process beyond just blanket "schools will evaluate you and consider you for interview without an MCAT score." For example, a school may try to evaluate people, but they will have to employ more stringent screens before doing so. This does not mean they won't eventually evaluate anyone, but they will likely be prioritizing people to evaluate based on their likelihood of getting a good MCAT score.
To clarify: even though many people who complete a secondary without already having an MCAT score do ultimately get an MCAT score, a significant enough number of people withdraw before completing their MCAT or get an uncompetitive score for a given school for it to be worth evaluating them all prior to getting an MCAT score. This means that they may be much more heavily weighing other factors and might be prioritizing review of people without MCAT scores based on those other factors (most likely GPA and other easily quantifiable numbers that correlate with MCAT). For those who aren't as competitive otherwise, they will likely be deprioritized or evaluated only after they do get an MCAT score.
Further, just because MCAT exams were delayed doesn't mean a score is going to evaluate people who have their score in October equally to people who have their score in, say, August. Someone who has their score and is complete by August is going to be a more easy target for interview invites, and schools will likely hold on sending interview invites to people who they aren't otherwise already sure about until they get the MCAT scores for those people. It's a significant investment to interview someone (even with virtual interviews), and schools don't want to waste interview slots on people who might wind up being uncompetitive due to having a poor score.
Making a blanket statement like "schools will evaluate you and invite you for interviews without an MCAT score" inspires false hope in people who think they won't be disadvantaged by not having a score until much later in the cycle. By all means, I don't think having a delayed score is going to impact people who do have their score by July or August, but not having a score until September or October is not going to be ideal for your application.