For the record, in Fed it is a violation "when" they step off. It doesn't matter how long they've been off (2 seconds as you stated).

I think it's a little different in NCAA...

Also, I generally enforce this in "real game" situations not wreck (they wouldn't understand) or off-season ball (it's not worth it).

Had his momentum carried him off the court & he delayed returning for a clear advantage... WHACK!