I don't know about you all, but I have to have a pretty regular amount of solving time in order to keep solving quickly. It usually takes me ~30 minutes to get in a groove, then I can stay focused for about 3 hours, and then solving and focusing becomes impossible. And I need to do this at least 3 times a week or I start to lose my ability to 'see' the puzzles quickly.
As a side note, this is why you see me with sporadically heavy months. I don't know how you regulars don't burn out.