Depends what I'm working on. Often I enter the flow and become engrossed in what I'm doing and at that point, the surroundings become totally unimportant.
Then, of course, there's the other times when I play a flash-game 2 hours straight..
As I read through some of the comments, I see that my arch-nemesis "time management" probably is one the reasons I'm sweating over this. Using the right amount of spare time effectively and letting it take it's time is probably key, but oh so hard to do.
When I say "slow down" I don't mean quit my day job, but rather put it off for a couple of years. Quitting my day-job feels like a bad move, but if things start working out I might take a day off every week to work on my stuff.
Then, of course, there's the other times when I play a flash-game 2 hours straight..