It can be delayed. We were there in a big storm- power was out in parts of MK and Tomorrowland was flooded. The first MSEP was cancelled. Wishes was 45 min. late. The Dessert party was a great place to be, IMO, while waiting for Wishes. They let us stay there, and keep eating/drinking- staying dry.
It is very common for Tink not to fly in August. She does not fly if there is the slightest weather issue. We have been to the dessert party six times, and she has flown only two of them.