If you count working on my book (the setting for which is what I'm running my campaign in), then it would be about...ohhh...2/3 of the time I'm actively doing something other than eating or sleeping (i.e. not while I'm watching TV, movies, etc.)...so, that translates to...hrm...
~30 hours a week...wow.
Not including the time I'm working on my book...
~15 hours a week.
Since I'm essentially homeschooling and don't have a job of any kind (yet), I have about...oh...8-10 hours of free time in a day. Unfortunately, all but one of my gaming buddies go to 'normal' school, and one lives about an hour away by ferry and freeway...so, we only meet about once every three weeks for 'real' sessions. We have occasional smaller-scale ones about half of the time that we're not doing one for the *main campaign.
*Only a 'main' campaign because the last two 'main' campaigns fizzled out, once due to me being a first-time DM with first-time players, and the second because the other DM got tired of DMing. This new campaign started up about a month ago, and the players like it, so that's good enough for me.