Im considering moving to switzerland (geneva or Lausanne) from Australia how much time in advance should I give before I start inquiring/appying for flats and units?

I would recommend starting up to 6 months before your move to switzerland.
One or two month before your move, everything should be ok.

You also need to bear in mind that the Swiss generally move only 3 times in the year: March, June and September. So those are the times you will have a bigger variety to choose from.