I think it was Terry Pratchett who said in some interview that a big chunk his work is done when he isn't actually writing. I understand exactly what he means. When immersed properly in a project, you could find yourself "working" at odd times, off and on all the time.
For instance, I woke up late this morning because it's the 4th of July and realized that soon I'll be starting the thriller aspect of The Durand Cousins. And then, while still in bed, I realized that a book really shouldn't become a thriller at the halfway point. If there is a "thriller aspect" I need a thriller thread all the way through the thing.
We no longer spend our 4ths at parades. Today we spent two and a half hours of it biking. Perfect time for work. I came home with some thread ideas, though without a complete thread.
But, remember, last night when I went to bed I wasn't even thinking in terms of a thread. So, actually, I did quite a bit today.