That isn't really the type of cert expiry they are really referring to, but consider this: The mechanism you describe requires a certificate revocation list, which is just another way of doing the exact same thing - using a trusted 3rd party to ensure you all agree on the parameters used to determine if something is trustworthy or not. That's not an improvement, and in fact, it is far less tolerant to network interruptions (a network interruption could cause a client to trust a credential that it should. Using time, it doesn't matter if the network is interrupted within reason, you can still determine if the ticket is still valid).
Remember, this isn't about you tricking your own clock to trust a ticket provided to you. You could choose to do that all you want. Its about the other party choosing to trust you or not. And YOU don't get to roll back the clock on their infrastructure. If you could, you could open a security hole just as you have described, which perfectly illustrates why NTP/Time Synchronization is so important.