Hi Kevin,
Thanks so much for sending your question to us here on the Disney Parks Moms Panel!
Looking at the schedule that is currently available for Magic Kingdom for May 31, 2015, it looks like
Wishes Nighttime Spectacular is not going to be offered that night because of the 7:00 p.m. closing time. If Wishes is a "must do" for your family, I do have some good news - it looks like it is scheduled every night in June starting at 10:00 p.m., so hopefully that will give you other opportunities to catch the show during your visit. You may also consider hopping over to another park on the evening of May 31st for one of the other spectacular fireworks shows. Epcot has
Illuminations: Reflections of Earth scheduled to begin at 9:00 p.m. and Disney's Hollywood Studios has 2 showings of
Fantasmic! that evening, at 9:00 p.m. and 10:30 p.m.
I hope that helps with your planning, Kevin, and wishing you a magical vacation!
Beth