I believe he served as the Athletic Coordinator as well. Here in MN and probably most places that is a lot of time going to different games/activities. Maybe in Texas it is just a title to have money funneled from other areas to help pay the head football coach.
Being a coach myself, the time away from family is real...I probably don't spend 90 hours a week (teaching all day, practice, and other duties can get close some weeks though), but it is a lot. Yes, being able to watch film anywhere is great, but that means I may not be engaged fully with family while I am doing that. Youth obligations takes up time after practice and other various things going on. Again, not saying I work 90 hours a week, but Texas football is a completely different beast and if he has other duties within the athletic program it could easily get up to that. Also, I would imagine he is not doing 90 hours in the off season.