Same here, except a 3pm cutoff has been adequate. That said, I usually have just one cup a day, and many (most?) other coffee drinkers seem to have more per day

Same here, except a 3pm cutoff has been adequate. That said, I usually have just one cup a day, and many (most?) other coffee drinkers seem to have more per day than I do. How long it stays in the body is about both how much coffee _and_ how late. If I were a heavy enough coffee drinker, maybe I'd even have to limit myself to before 10am only, to get sleep improvements?