Just out of curiosity, was there a reason given with the request? If the child is eating the normal amount at your scheduled times, then there should be no need for an additional snack. Especially for 7.5 hours. And even then, at 12 months+ a child is usually capable of deciding what and how much they want to eat.

Did you explain the reality of daycare scheduling to the parent? Most people don't really understand what it's like during the day and maybe just a bit of an explanation of the time required for snack and lunch would let the parent understand. Snack might be eaten in 5 minutes, but there's 10-15 mins prep time, and 10-15 min. clean up time after too. This is not even taking into account the cost associated. If you are giving 1 child an extra snack, you're gonna have all the kids wanting it too. Even if the parent provides the snack, do you allow outside food to come in? I personally don't. Not since the time the parent brought "breakfast" for the kids - Fruit Loops.