Well Psycho Killer (Talking Heads) took all of 10 minutes but Darling Dear from the Jamerson Motown book is still a work in progress i.e. I've got the notes and note values even the phrasing down, but the tempo is at 2/3 performance tempo. So the answer is material dependent. Even within the same group's material there are varietal difficulties. THE Beatles', tune Birthday, is another that took less than a half hour, but Something, took about a week.....taking out time for meals of course.