The quickest I saw them done was 1 month per 7 subjects, the guy then sat the 7 exams, took and did another 4-5 weeks study for the next 7 subjects, then sat the exams , about 3 months start to finish he took which was mainly due to fitting in the fixed exam dates the UK system uses.
This guy was a 737-400 check and training, about 15 000 hrs in his late 40's, highly motivated to take up a well paying high ranking job in a major carrier in Europe.
Depending on your experience you can do this too, its doable with motivation, but if you dont have some of the regulatory requirements you may be stuck for 10-12 weeks per 7 subjects as per the laid down minimum study hours of JAR land for the theory. Contact a school like more well known school like Bristol (
www.bgs.gs ) for a timeline for training based on your flight experience.