I'm confused, I am in the middle of the process of joining a UAS, and unless you are going for a bursary, you DO NOT have to pass OASC. You just have to pass the medical and the aptitude tests (if required). You have no interview at Cranwell, only with the CO of the UAS in question. As you are going up in November, it would suggest to me that you are applying to join the RAF(VR), as screening of bursary candidates doesn't start until January. So, brush up on the speed/distance/time stuff, and that is all the preparation that one can do (Of course you will need to prepare for the interview with the CO).
Good luck, TMA