If you can stand them at the door ringing and knocking and it wont wake anybody in the house, then let them do this. Answer on the 4th knock or 2nd, 3rd doorbell ring. rush to the door, say that you must not have heard them, as you are still getting ready for the day, or, better yet, show up with a towel on your head and ask "is it 7:00am already?? I thought it was only 10 mins to!"
if they cant get the hint after this, you'll have to ask them straight out, please dont come until my scheduled 'open' times.

Im a wimp when it comes to confrontation, so any 'subtle' hints, I'm all for them!