Painting is slow work for me. But meditative. I fall into a kind of trance while I'm working. I usually listen to episodes of This American Life. They go for an hour so at least when one is finished I know how much time I've spent on the painting in one sitting.
I considered logging the hours I spent on one painting and I actually started doing it with this latest one but then lost the motivation. I think it might be dispiriting to actually know how long it takes, from start to finish.
I think I would rather just enjoy the process. Getting lost in it.