Just check the time on his flight, it has to be before 23:59 AEDT on the 23rd.
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Thanks, medhead. Hubby will be flying out of London on 23rd December on QF32 which leaves LHR around 11am. So, I think he should qualify for the double ff points one way from LHR to SYD. He is leaving SYD for LHR on 31st December.