I think the sooner you do it the better.
I am the opposite of you. I left the forces in 2001 and decided to transfer my pension fund into my new CAA pension. I did it before I qualified in my new job, whilst on the training pay as the way it worked was you bought x amount of years based on what your current salary was, therefore on a lower wage my transferred pension gave me more bang for my bucks.
I believe buying extra years will be the same for you as you have to buy at a price comensurate with the monthly pension contribution which obviously increases with yearly pay rises as it is a percentage of your salary.