Think about a time-based one-time passcode (OTP). Every 30 seconds you get a fresh code and the attacker tries to guess that code. There's usually a validity window of one or more OTP, so the attacker needs to guess one of several possible currently valid OTP.

This is a popular trick in CTF exercises and it's pretty quick if you can make 1000 guesses per second. Takes a couple minutes until you're in.