The Kiss is wonderful.
I dont know if you can get a CM to tell you when they'll do it (if they'll even do it) and I dont know that the CM is going to be correct, even if they tell you.
often times, it's a while after the park officially closes, and Main St is still open. It's a very touching thing when they do it.
Basically When you wish upon a star starts playing and the castle starts doing some really cool things with the lighting, and then a voice comes on and talks about WAlt Disney's dream and things like that. Then it ends with a playing of When you wish Upon a star (with vocals) and just really caps off a great great night. Don't be surprised if you well up a little when you hear it.