I agree, though a lot of the time what I need to do requires just thinking about stuff, sometimes I need to plough on and just do stuff. 6 hours of coding something, writing, whatever. When that happens I just do the work.

I'm lucky in that I can work the hours I need to work. Last week I did days that lasted 4, 6, 1.25, 1.75 and 4 hours (the 1.x days I had other stuff on).