I don't wait. We follow our schedule. If they are not there while I am prepping snack then they don't get any, if they are not there when we start craft they don't get to do one. I would send out a notice to parents stating exactly what you told us - that inconsistent drop off/pickups are disruptive to your schedule. Ask that if they are going to be picking up or dropping off at a different time to please send you a text. Let them know that you will be sticking to your schedule and any that come during or after will not get to participate.