We're coming to NY end of April and would sooo love to to see this, but from what I see on ticket master, it only runs Saturday mornings...and we won't be arrving until early afternoon. We're only staying until Tuesday. Do they ever add extra shows?
Every so often they add an event on Wednesday, but it doesn't seem that would help you either.
It is basically a pop-up museum for Wicked: they have memorabilia such as costumes worn by Kristin Chenoweth, Idina Menzel, and Joel Grey; masks of former cast members; stage props such as a map of Oz, the letters written home, tests taken at Shiz; and they show a short film (or two, I can't remember). It's pretty cool to hear the cast members' stories, such as the fact that there is "wing etiquette" backstage for the flying monkeys. So if you happen be in NYC another time when you can catch it, I would recommend it.