Sorry for the non-answer here, but I take a different approach: I work when I feel like it.

I'll try getting stared on the actual work, whether I want to or not (you have to overcome that initial mental inertia). Then once I'm about half an hour in to the work, if I find myself watching the clock or thinking about how I should go check my RSS feeds, I'll stop and switch to my list of more mundane tasks.

Just summarize the first half-hour of your work, and if it's crap, move on and come back to it later. If it's crap, you broke even, and if it's not you've saved yourself a half-hour wasted on Quake.