A House of Representatives election must be held on a Saturday prior to April 16, 2005. However the Prime Minister has strongly indicated it will be held during 2004 and he would be heavily criticised for breaking convention if the Government's term were to extend more than a few weeks beyond its three-year anniversary on November 10. The earliest date on which a normal half-Senate election may be held is August 7. A double dissolution election may be called at any time before August 11 for a date no later than October 16, but this is not anticipated. A House of Representatives election before August 7 and a separate half-Senate election at a later date deserves mention merely as a technical possibility. The announcement of the election must be between 33 and 67 days before it is held, but governments have kept campaign periods short since the Hawke Government performed disappointingly after a seven-week campaign in 1984.
I doubt there'll be a double dissolution. About the only thing I don't doubt is that the general election will be held before the US presidential election.
The Poll Bludger lays it all out, including various trigger dates. Assuming the Man of Steel does not indulge his taste for the crass with a 911 election the most likely dates remain 23 and 30 October.
We really, really need to move to fixed dates for federal elections.