Artists are professional noticers. The job starts before you ever pick up a brush.

Most of the work happens away from the desk, during hours that do not look like working at all. Walking, waiting, overhearing: that is where the material gets gathered, and by the time you sit down the gathering has either happened or it has not. Treating the desk as the whole job leaves you arriving empty.

Count the noticing as work rather than as leisure you should feel guilty about. Keep a way to record it, and protect some unoccupied time the way you would protect a session.