I didn't go to Bristol but here is my experience of doing it on a self study basis. Its a bit hard to say how long it will take as it is down to the individual. Some of the subjects will take no time at all to study (eg: the 2 comms) whereas others like MET, GNAV or Air Law can be literally ball aching to get through the volume of information you need to retain. It will also depend on your approach to study. I hit the books making notes as I went and then about 1.5 months before my exam sitting I was on the Bristol Online database going over and over and over and over (get the picture) the questions until I was getting on average >90% in the mock exams. Then hit the brush up course and kept on the database at nights in between doing all the homework that you will be set. Got me through with a pretty high average.