That's the bad part... the drive can be done in about 14 hours with minimal stops and no major traffic issues.
But I typically count on 16 hours of drive time including stops.
For us, it works well to leave in the evening and drive all night. If the kids will sleep, we don't have to stop much until morning and we can be at the resort by the middle of the day. In theory, you take that half day to just hang around the resort, take a nap and rest up. I never can quite sit that still once I'm there though. And another 4 to 6 hours of driving time would definitely make that a lot more difficult to do.
I did go on a trip one time with some friends where we left on a Friday after work at 6pm, drove all night and we were at Universal when the park opened Saturday morning. That was 11 years ago. We stayed in the park all day, and it ended with a Lynyrd Skynyrd concert next to where Rip Ride Rockit is now. It was a lot of fun, but I'm not that stupid anymore. I went over 40 hours straight without sleep on that one.