You can get in with 250 hours just fine, but the interview process can be a handful. The time they spend training you in Adelaide, however, may vary in length depending on your experience.
If you are successful in the selection process, you will write the HKCAD ATPL exams in Adelaide (they are basically EASA questions). If you hold an FAA license, you will have to go through this process as part of your pre-employment training.
Someone also asked what the SO does. You are a cruise relief pilot. You operate the left or right hand seat above 20000 feet. In the actual operation, you don't operate the takeoffs and landings, although you will get to do so in the simulator. You also normally do safety checks and make the bunks. The current guestimates for being in this role is 4 to 6 years (may go up or down depending on industrial issues). It has its pros and cons.
If you are considering CX, I think it will be important to consider that at present, Hong Kong is the most expensive city in the world and buying a house is next to impossible until the next major catastrophe. Not to deter you, but I encourage people to be careful and excercise sound judgement.