AO interviews tend to be held over the whole one day, so if you are successful expect a long day. They wont expect you to fly up for every stage. Just from past experience you go through about 2 or 3 stages on the first day, then it's the medical and security check sometime after that if things are going well. Medicals have to be done through a GP who specialises in airline medicals and there are several in every city, you send the resuts to the Qantas doctor (it's a tamper proof document). Just a word of warning, getting the go ahead for security and medical checks, which are at you own expense are in no way guaranteed employment. I know many people who made it to this stage with no problems and still didn't make it. Good luck.