UA will cancel all forward bookings after you miss the FIRST leg of an itinerary ticketed on UA paper AFAIK. Hidden cities and security issues etc, etc. You say the tickets are issued by UA so be mindful of that.

And I agree there is no way known to get off QF domestic and onto UA It'l in an hour. Forgedddd it. The 2 terminals are miles apart and you must clear oz customs FIRST before you get anywhere near security, and there are often lines at both. And UA has an extensive hand check of EVERY person at gate as mentioned above.

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~ Glen ~