I charge $1 for every minute past 5. At 5:20 it is a full days rate. I also stress to parents that I have evening commitments so pickups are expected BEFORE 5 (as it takes a few minutes to get their child out the door). I also start texting a few minutes past 5 in the event they are late. That way they realize it is not acceptable. I have had a few issues nothing too major but I make it known that even though there is a fee that it doesn't mean I accept late pickups. I also have it stated in my contract that consistent late pickups may result in termination.
My late fee also applies to when I have to close early. If I close at noon one day that means all kids need to be gone BY noon not after. Late fees begin at 12:01.
I don't work with schedules pickups. I am open until 5 but if someone normally picks up ay 4 but doesn't get here until 4:45 that is fine, no late fees.