If the last parent picking up is coming at your close time and you know they could come earlier without it being a problem then changing your working hours is the other option to close sooner such that late fees will also kick in sooner such as closing at 4:45 instead of 5 and especially if you know she can be there by 4:30 if she wanted to be.

Then if you get a family needing later than that you can negotiate the fee accordingly but the official close time still stands.