I average roughly the same. The last time I had a dayjob, I did about that amount of work each week, then stepped it up considerably in the couple weeks before a big release.

My problem is that, while working on my own stuff is fun, I'm often too pissed off about the dayjob when I get home each day and I tend to ruminate.

Sometimes I just end up not doing a hell of a lot. But other times I can salvage the rest of my day -- I'll take a quick shower and nap, then plan on spending 3-4 hours at my favorite cafe with a specific set of bugs or features to work on before leaving.