At some point every Saturday, while watching a college-football game that seems like it started forever ago, you might think that games didn’t used to drag on for so long. It isn’t just your imagination: College-football games really are getting longer.

In the 2008 season, after the NCAA passed new rules meant to make games shorter, the average time of a regulation game was 3 hours and 11 minutes, according to Stats LLC. Since then, that number has ticked up almost every season. It peaked at 3 hours and 22 minutes last year,...