Stuff from the West coast of the US generally arives quicker. Most of the post to Australia leaves the US from California and gets trucked or flown there from central US if need be. Not sure if any leaves the East Coast direct.
I get West Coast stuff within 4 days for normal airmail at its quickest and 12-14 days for the longest for other parts of the US.
get it sent airmail registered and insured. For a $500 card it will come to about $14US. They will send you reg# and you can track the package. It will be fully insured for the $500US too. It will take a week or so to get here.