When this happened in June, there were delays of 1.5hrs to get out. They don't do it all day, generally for 4hrs or enough to get into the headlines. So when you arrive, it might be totally normal.
http://www.skynews.com.au/news/top-s...b-airport.html

I wouldn't change my whole itinerary for this if it is a big hassle. Things can change quickly and the strikes might not happen. Or they could be a bit worse.