So I was supposed to retake my MCAT on 7/18/2020, but cases in my county have spiked and they're tenatively moving to lockdown the county starting this Friday so I got an email from the AAMC saying my MCAT date might be canceled. So I preemptively moved it to the first week of august to ensure I got a date. However some people have told me schools won't wait for my new score if I send in my secondaries (my first score was a 504 and none of the schools I applied to will screen me out for this score). I just wanted to see if anyone could shed some light on the situation or if I should wait to submit my seconaries til august? Thank you!
The premise of your question is unclear. If your county is moving to lock down and your 7/18 test is actually canceled, why would you think you'd be good to go a mere two weeks later? You won't be! Lock down is a big move that everyone is looking to avoid, but, if it happens, it won't be reversed in two weeks. All the problems we are having now is because lock downs were lifted in less than two months!!!
If you need more time, that's one thing, but otherwise I'd have kept the 7/18 date. With respect to schools waiting, you have misunderstood what people are saying. Schools can see that you have another score coming, and schools are certainly free to wait for them (most schools will), but that doesn't mean they have to.
Bottom line -- if you don't want them to review your application until they have your score, why submit a secondary before then? If they don't have your secondary, there is nothing for them to review. I get that you want to save yourself a place in their queue, by submitting before you want to be reviewed, but that's not how it works. You control whether or not you are reviewed without the score by controlling when you submit your secondary.