With the exception of the initial release of a new macOS, iOS, iPadOS, WatchOS, or TVOS (ie macOS 12.0) public beta testers will get access to each beta version within 24 to 48 hours of the release to developers. And generally all of the various Apple OSs will have a beta release within the same 24 to 48 hour window. So today I installed macOS 11.3 beta 4, iOS 14.5 beta 4, iPadOS beta 4, WatchOS 7.4 beta 4, but I haven't gotten around to TVOS 14.5 beta 4 yet (maybe this evening).

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein