The official last posting date for regular mail to Australia isn't until 6 December, Smow, so your card should arrive in plenty of time. (That's assuming that, unusually, you didn't choose to use 'International Economy', so that it went by ship. The last posting date for that service was 13 September!)
I've been known to not even buy my Christmas cards until 3pm on Christmas Eve (including those for overseas delivery), so it's not unknown for my cards to arrive just a little bit(!) late, but I usually post the few that I send these days about a week or two into December. The only exception is the card that I send to my friends in Italy, as Poste Italiane's service is appalling, with anything sent to of from Italy often taking a month (or even more) for its journey. (I won't have to bother this year though, as one of the couple arrives in England on Saturday for a couple of weeks or so here, so I can simply hand over the card in person).