72 hours begins after your transit pass is approved?

I just got off the phone with United and the rep looked into this transit process. She said they were told that the 72 hour transit time period begins when your transit visa is approved, not when you land. My current flight is a couple hours over the 72 hours. So If we waited in the airport until there was only 72 hours, and then when to get the transit visa, would that work?