I'd say the average is around 8 months but budget for a year. I wouldn't put too much stay on people's background educationally. I know it has been done to death but you cant really tell too much by that as it is purely based on so many factors.
It is so specialised and you cant blag any of it like Degrees and A-Levels as it is simply a pass or fail.
I wouldn't worry too much, the only way you are going to fathom how hard it all is is when you get there as different people will tell you different things.