the only limit is in the "blackout" period which covers from midnight of the Wednesday before polling day (always on a sat here)
worse than that is that our pollies have the absolute best of both worlds. they have access to public funding but there are NO caps on spending and NO guidelines as to what is and isn't political advertising (both parties tend to use incumbency to run copious "government" ads that are nothing more than party political broadcasts.
Also in Oz unlike the the UK and many other western democracies there is no compulsion for TV stations to air the ads at a cheap rate or to provide free spots (the abc does as part of it's charter but they're rarely used as no-one wants to make 5 minute broadcasts anymore it's all about 15 second soundbites)
so we have a situation where the public is inundated with ads that contain ZERO policy information cost an absolute fortune and contain pretty much any amount of bullshit you like.
Lynton Crosby is a master of dog whistle politics and is worthy of any amount of disdain any sees fit to send his way - one of his big "wins" was the demonisation of a bunch of refugees on the Tampa - interesting to see the Tories have gone for a bash reffo's theme as well!
you might find this interesting
http://www.safecom.org.au/2005/04/lynton-crosby-globetrotting-spreading.htmif you're really interested a recent Australian book looks into political advertising over the last 50 or so years and while quite repetitive is pretty interesting..
The Persuaders: Inside the Hidden Machine of Political Advertising
by Sally Young