I am shooting something next week and they want to recreate this look:

The Watters Family on Vimeo

Is there a plug-in that gives the look? Can you mess with the frame-rate in post?

The Posterize Time effect, with or without changing the Speed/Duration, will do what you want very easily. Unfortunately, Posterize is not one of the GPU accelerated effects so you'll likely see preview file renders occurring as you go along.