How long does it take for people to get acquainted with the Wii fit?

I'm currently on a committee that is planning to hold a event featuring multiple workshops on Nov 6 to promote healthy diets and regular exercises in adolescents. One idea for a workshop was to show how one can maintain a healthy daily regimen using a Wii fit or perhaps the new Kinect from Xbox (the game being Your Shape™ : Fitness Evolved). That's where my question comes in. Since we are expecting 150 or so people and most likey everyone will want a chance to try one of the game systems, what would be your best estimate on how long it would take for people to get familiar with the Wii fit or Kinect. Factor in the average time to play through a regular exercise routine and other necessary factors if needed. Keep in mind that these are 12-18 year olds, so there are bound to be people who are farmiliar with those devises.