we used to leave Millington about midnight and make it to Waco by 9 or so...about the time all the kids woke up, which was the reason for leaving at midnight...
making the trip between Millington and Knoxville more then once, I'd say it would add another 4 hours or so to that.
So, best guess, I'd bet it would take y'all about 13-15 hours, depending on construction (there always seemed to be construction around Little Rock) or weather....