Every time I plan to Oz I'm 8 hours or more away anyway!! So I have no choice but to use a TAF.....
ACMS,
Of course you do, but withing AU, and 3 hours of the destination, the TTF supersedes the TAF, the TAF remains valid for the rest of the flight, including an alternate if it is outside of a TTF for the arrival at the alternate.
Put another way, in AU you must get a TTF covering your arrival, you can't ignore it and hope it will go away.
ICAO-wise, the same thing is true, it is not valid to rely on a "favorable" TAF if a TTF indicates a deterioration, because the far more recent TTF will be based on current (as opposed to maybe 20+ hours old TAF data from the time of the original forecast).
The obvious question re. the above comment is: "Why would you", but sadly the aviation business these days is full of "bar room barristers", at the expense of common sense, sometimes referred to as airmanship.
Tootle pip!!