I love all of Beachbody's products, I actually try a bunch of them and blog about them each day if you're interested. (msg me
By the sounds of it, you're most interested in trying out Cardio. You'll get amazing results with it even by the time the 12 weeks roll around, so don't get discouraged that it's 20 weeks long. But if you're really looking forward to "finishing" a program in 90 days, P90X was what kick started my fitness journey. If you're looking for pure cardio though, I'm really enjoying Insanity right now as well, and that plan is only 60 days (8 weeks).
I suggest trying it out for a week or 2 and seeing if you like it, because at first some of the moves may feel awkward, but I promise you'll get the hang of them. If you still don't like it after 2 weeks, see if you can return it and try something like Insanity instead.