Honestly I think one's success in such accelerated programs depends on his or her personal aptitude and academic stamina. A buddy of mine completed his multi rating in four days from scratch; that is, going through the written, oral and practical tests, and passing the checkride with flying colors. Certainly the instrument rating is one of the toughest ratings to acquire as a pilot, but as I said earlier, it all depends on you as the individual and the overall expertise of the instructor who in turn will need to break down the material for you in a way that you can digest it within such a short amount of time. I personally wouldn't choose such a route, but that's just my individual stance. First and foremost, know yourself. If you can assimilate information within a relatively short amount of time then go for it! If not, well...That's pretty much my two cents worth. Cheers!!!!!!!!