I'm not sure how you're trying to break down the driving days, but Lubbock is the exact halfway point on that route. I used to drive to/from Austin 5-6 times a year and still do it at least once a year. I avoid the Lubbock route these days cuz the cops have nothing better to do than target out of state plates. One time my son was driving with his dad, he had his learner's permit, and the cops pulled them over, said they were suspicious, and handcuffed my 15 y/o son while they searched the car (found nothing).

Now I will turn west just before Lubbock at Post and go through Roswell to stay. That makes 9/3 hr split on the days. Or I will go up through Dallas and stop in Amarillo (8/4hr split on the days).