I might be a bit of a hard-ass compared to some of you! My listing has 11am checkout. It's in the house rules that they need to arrange early check-in or late-check-out prior to reserving.
The day before check-out I send them an e-mail with checkout instructions, including a reminder about 11am check-out. If I don't have back-to-back bookings or don't plan on cleaning that day, I'll let them know a later checkout time - usually 1 or 2pm. Almost all my guests have been great at leaving on time.
A few have stayed longer; at 11:30 I'll knock and start bringing in my cleaning supplies/stripping beds. It's all friendly chats, but my presence is clearly sending the "you don't have to go home but you can't stay here". I owe it to my next guests to have the place ready when I said I would.