Mistify is at 10 pm after Shamu Rocks which starts at 9:30 pm. I'd find a spot between the Sky Tower and Sea Fire Inn restaurant if you can by the time Shamu Rocks lets out.
How long does Mistify last? Our hotel shuttle does its pick-up at 10:15. It doesn't sound like that will work out very good if Mistify is at 10 PM. Is there a way to make a quick exit in order to beat the crowds?