well according to ChristmasPrincess's blog the entire design rehab lasts 30 days :p so we have about 23 left to go I think :p that's if more then one person is left or else it will end as soon as there's only one person left standing... and I think it's per group too not quite sure though :/ more info here:
http://www.tengaged.com/blog/ChristmasPrincess/2102861/im-gonna-make-you-go-rehab