I have my Mutants and Masterminds group that I GM which is for six to eight hours, then my D&D 3.5 group that I play for four to five hours. I also have another D&D 3.5 group that plays once per month or so, and that's between five to ten hours depending on our schedules.
So collectively I play ten to thirteen hours a week of gaming on a given week.
On a week with my extra group fifteen to eighteen hours.