Probably 10-12 hours, I think for work. My brain doesn't have to think about common tasks: Walking, cooking breakfast, speaking/writing conversationally, driving etc. I can be thinking about something else while I do those, or zoned out and not thinking about anything at all. I actively think when I'm feeling contemplative, about to go to sleep, meditating, and also when I'm reading/listening or doing something tricky like writing concise prose or figuring out a math or programming problem. Living alone it's fairly easy to spend a whole day going through the motions, but I try to avoid doing that.