If you are waiting for them to call you, don't sit around doing nothing. Keep working, flying or doing whatever you do. Sitting around being idle does not make you feel better, and it certainly does not help your interview performance. Active minds perform much better under pressure than stagnant ones!
Having said that, as SW1 has mentioned the time one waits between applying and getting called in for Stage 1 does vary. After applying, I waited for 6 months and 1 week before getting invited for Stage 1, which was held 2 weeks after I received their invitation email. Then I waited another 2 weeks after Stage 1 for their invitation to Stage 2, which will take place about 1.5 months after I was called.
There is no standard pass rate for Stage 2/3 candidates; anyone who clears the hurdle gets past. I remember hearing someone once saying that Cathay has a cadet spot ready for anyone who passes Stage 1, provided he/she can perform to the expected standards in Stage 2 and 3. That said though, the attrition rate is quite high, as you might expect.