"I think generally speaking, we want to see shorter events… not in every circumstance," France told the group, "… It's no secret that attention spans, especially with the millennial fans, are changing, and we all know that. But what we like about it from our standpoint is it makes the actual racing event better because there's no lull in between the beginning and the end, or there's a lot smaller lull, so teams have to compete."
France said a longer race doesn't necessarily allow drivers time to relax "but they're not as pressed to be up front at a certain time. "But if you shorten it, they will, and we've seen that when we do shorten it," he said.
"We tend to get better (quality of races), and we measure that by lead changes and how close the winning margins (are) and a lot of different metrics that we use. So we've got a pretty good handle on that, and … a 400-mile race will give us, most of the time, a better racing competition, and that's in addition to the time spans and attention spans of millennial fans; those two go together for us to shorten it up somehow."
France didn't rule out dropping the length of a race below 400 miles, but noted that any such decisions would "also depend on if there are any format changes that we'd be willing to consider, that we look at all the time, that we historically haven't done." (NASCAR.com)