a few ways - first the schools themselves often provide some sort of date on their admission page..
second here on CC they keep a calendar of release dates updated based on when school “officially” notifies (usually per instagram or email)-and prior years are pretty reliably an indicator of next years (w/i a few days) - once in awhile they will throw a curve ball. e.g. one of my kids schools WPI, changed EA from late January to mid-December this year! That is very atypical though. (they also, apparently, added ED only like 5-6 years ago, though, so have been experimenting? EA used to be in December back then)
College Decision Dates: The Official 2025-2026 CC Calendar you can scroll back!
last if you want to be really OCD (like I can be) you can go to specific schools instagrams…they often post the day decisions are released or a few days before.