It is essential to apply in the early round (“EA”, “priority”) at public universities that have it, because they take almost all their applicants in that round. It may mean “app in” or “app, test scores, everything required, in and processed”.
Typically that’s Nov1, sometimes Dec1.
In addition that may well be the deadline for Honors college and scholarships, or there may be an Oct15 deadline.
Before that date, some public universities go on a first come first served basis; some pre-sort and some clearly qualified/clearly unqualified students may hear early while the 90% that require careful review have to wait.
For private universities, the level of selectivity matters, too - if 70-80% applicants are admitted, applying well before the EA deadline could well result in an early acceptance. At sub-25% acceptance rates, universities are likely to have a date where everyone hears at the same time.