I have some parents who will occasionally TRY and drop off earlier or who pick up a few mins late or right at closing.
This is what I do: I keep ALL my lights off. Doors locked. Its a ghost town in my house until 7:00am. Last week I had a mom knock and knock (I don't have a doorbell hehe) and I stayed upstairs and ignored them until 7:00. When I opened the door I said "Oh sorry were you knocking? I was upstairs getting ready, every minute counts here in the mornings" and that was that.
For the lateness I have my lateness policy posted on my whiteboard which states you get 3 chances then are charged $1 per minute payable by drop off next morning in CASH otherwise child is not accepted into care that day.
I also do my best to have the kids all ready in their coat, shoes etc for when parents pick up. When parents arrive right at my close time, I make a point of saying "Sorry can't chat, headed out the door".
Usually they take hint. Still happens from time to time.