I think it might be long time in Winter. That said, you are offering service that maybe you not normally do. The parent have understand that you operating group care and although try make timing work for all, there have be some compromise. As much they might like to think you able to time think exactly as they want, it not always possible. Other parent might like 15 min adjustment to meal and lunches but can't always be done.

They know there reason for timing and they know you need be somewhere else for other child. They have now decide if they can live with the offer or not but it not sound like something you able to change.