When I am in "writing mode" I try to set myself on a quota system. Typically 1000 words / day is my min quota. I find that's a fairly easy number to reach and on a good day (note: they're not all good) it can be as little as an hour's worth of work. That being said, my quota is 1000 but I'll often set a goal of 2000. Anything above that is gravy