The experience takes a couple of minutes and they let about 25 people into the shop at a time. After the experience, the wandkeeper's "associate" takes the group into the Owl Post where the person who was chosen to participate can either buy the wand that chose him/her, another wand, or no wand at all. In addition, everyone else can browse wands to purchase (including the experience wands) and an associate will gladly assist you with finding a wand that is a perfect fit.
I know I said I'd stop, but realistically I don't really mind continuing the wand discussion because there are a lot of misconceptions and a little discussion never hurt anyone. That's what forums like these are for: to discuss the WW and express hopes, concerns, and impressions. One of the main things I've heard on here is that UO "advertised" Ollivander's as an individual experience. They didn't. They talked about it being unique. It is. They spoke of it being intimate. At 25 people only, it is. They spoke of how the "wand chooses the wizard." It does. No where did they say everyone would actually experience it, only that everyone would have a chance to see the experience and everyone would have the ability to select a wand (or have one selected for them). They will. All of the speculation about individual experiences, or everyone getting a chance to be chosen were conjecture on the parts of all of us.
I can confirm, although I cannot and will not reveal my sources, that the way the wand experience was done in the TM preview was in fact how it will be for paying guests as well. They're still working out queues and how to control the crowds, but only up to three people will actually have a wand choose them. That's all the wandkeeper's script allows at one time. That will hopefully keep too many situations where one sibling gets the experience but another doesn't from happening, but it won't accommodate every child or adult in the room. Sorry, but that's how it is.