I applied in January 2006, but have been deployed ti the middle east for 2 months, and also left it quite a long time between me tests and interview (about 7 weeks!)
I know of a guy who applied in Febuary, and he started the college a few weeks ago. So it really depends on you, and how quickly you can go to the various stages.
One thing that I will say, is don't leave your application too late, as I'm sure that NATS can't keep up the current rate of recruitment for ever!
Good luck with you application
Ian Dickson