I guess I'm a bit more demanding but given the plane was missing from radar and out of communications in a fairly populated area, with at the time, a belief that 7 Aussies and 2 Kiwis were amongst 239 missing people (a major incident in anyones book), just might have spurred immediate action. The Defence Force would know without hesitation which assets were available to scramble and from which bases and I believe there would be standby crew available for immediate deployment. The planes locale was also decided early on that it would most likely be over water which means a) given loss of power and gliding capabilities, there could be survivors in the water; and b) it's possibly international waters anyway, surrounded by "friendly" countries and with a flight time of about 6-7 hours out of Darwin.
Australia spends a fortune on military exercises, so even if this did turn out to be a red herring, surely such an operation can easily (and rightly) be chalked up to an exercise that possible had a real life saving purpose?