Place your order before 10am for urgent deliveries using Express Post, which guarantees overnight delivery to addresses within the Express Post Network. (Please visit the Australia Post website for a list of delivery postcodes in the Express Post Network).

You can choose the express post option in "Shipping Method" (step 2) of the checkout. 

Scroll down to view the postcodes here: http://auspost.com.au/parcels-mail/delivery-areas.html
Express Post is a flat rate of $22.99 per address, Australia wide.