The fact that the parent has contacted you now shows their concern and that they acknowledge the importance of their child being there. There are parents who will take that vacation and not let you know in advance at all. I used to teach in a town with a single large industry. The parents did shift work, and signed up for vacations in the order they were allowed to. For some parents on the lower end of the totem pole, a week in August was the only vacation they could get. When they told me that, I told the student I'd see them the next week when they got back and to bring me pictures. It made for good relations with parents, community, and that industry which was, by the way, very supportive of our band program.