Indeed, I've had mixed success over the years as Platinum.
However, the full detail is listed under
Travel Benefits:
[TABLE="class: basic, width: 718"]
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[TH="bgcolor: #F5F5F5, colspan: 2"]Flexibility to catch an earlier domestic flight[/TH]
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[TR]
[TD]When can I request to move to an earlier domestic flight?[/TD]
[TD]If you are travelling on a flexible Qantas fare (Fully Flexi and Flexi Saver fares booked in B, H, K, L, M, V or Y in Economy or C, J in Business) and you arrive at the domestic airport earlier than planned, you can request to be moved to an earlier available domestic Qantas flight without paying any fare differential, even if there are no seats available in the booking class on your ticket. To move to an earlier Qantas domestic flight, a seat in the same cabin on the same routing and day must be available and the request can only be made for single sectors departing from the airport where the request is made. Standard
check in and flight closure times apply.[/TD]
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[TR="class: last"]
[TD]How can I request to be moved to an earlier Qantas domestic flight?[/TD]
[TD]On the day of departure, you can request to move to an earlier domestic Qantas flight by visiting one of the Qantas Club/Business Lounges or the Qantas Service Desk at the airport.[/TD]
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