Hi, I am also going for Int Officer and had my CBAT at the end of May. The advice from HOPEFULPILOT was spot on. We started our testing at about 7.30am and I finished at 2.30pm. I was the first to finish which was very worrying, I thought I had done it all wrong! I also came out of the testing session for my first 5 min break and felt a complete failure, was ready to go home right then as I knew I hadn't done very well, however, I passed everything with really good scores so my advice is just give it everything you have. It is an aptitude test so there isn't much prep you can do in advance as that is part of the point of the tests. They want to see how you can cope with the instructions then putting them into practise. Again all I can emphasise is read the instructions thoroughly, take the breaks when you get them (the computer will automatically tell you when to take them so don't ignore them) and take a water bottle. The tests do depend on what role you are going for as the pilot candidates had to do a couple more tests than I had to do.
You do need to wear a suit in the mess and I wore smart trousers and shirt for the actual testing day, pretty much everyone was in suits/very smart dress all the time.
I had my CBAT on 1st June, filter interview on 12th July, medical on 2nd August and I am booked on OASC for 21st Sept to give you an idea of timelines.
Good luck!