It's not difficult to enforce, they won't let you in if you try >3 hours before your scheduled departure time. It's not like its a max stay of 3 hours whenever you want and you carry around a timer.

However, the 3 hour limit doesn't apply to connections, if you're a Platinum card member. Also the 3 hour limit doesn't apply at all to Centurion cardholders (which the OP says they are), so it's a non-issue in this situation.