One of my coworkers (like you, at a government job involving software) had occasionally said "you can only read Dinosaur Comics so many times before you have to find an open-source project to start contributing to".

We created a lot of our own work; we were given a lot of leeway to find and fix problems ourselves, even if the problems hadn't actually appeared yet. We were encouraged to find research areas to work on, and use our time to do that as long as it didn't detract from our other duties, which probably only consumed 4-10 hours a week. So, we had license to work as diligently as we wanted, and for the most part on nearly anything we wanted. However, we generally found that most days, we weren't able to be productive for more than 4-6 hours, and ended up spending a lot of time reading webcomics, writing toy programs, and drinking tea in the break room.

I think for most people, 30 hours of high-quality creative work a week is about their limit. I'm sure some people are exceptions, but some of the most productive programmers I know (from FOSS projects I worked on to government jobs I held and even a stint at Microsoft) spend about half their "day" goofing off.