The time is usually an estimate, or the best case scenario in my head. If I have to stop and add more time, I do. But 10 hours is probably what google maps told me it is. I drove straight 9 hours or so once, I think I stopped twice to use the bathroom/get a snack. Got there at 2am. It was rough, wouldn't do it again.
For that particular drive I was on Adderall and smoking a lot of weed so hyper focused paranoia prevented that. However, when I was following tail lights at 70mph through the mountains in a downpour and the windshield wiper came off, the pucker factor was very high.