Couple of years ago drove straight through from Ohio to Minnesota, 800+ plus miles in one day, a lot of it in heavy rain. Think it took about 14 or 15 hours.12-14 hours. That's at the extreme limit of what I felt comfortable doing. Haven't done that in years though.
Surprisingly, I was not that tired at the end, but was getting drowsy/losing attention. Had a new car with adaptive cruise, which was a godsend.
I have also made the trip a couple of times in one day without cruise, but I was a lot younger then. That was a killer; dont think I would be up to it now.