There is no legislation or regulation that restricts the number of flights that can fly over an area.

Sydney Airport has a legislated cap on movements that restricts the number of flights to a maximum of eighty per hour. This includes both arrivals and departures. 

Airservices is charged with implementing this cap by counting movements per hour on a rolling 15-minute basis.  If the cap is at risk of being exceeded air traffic controllers will take actions such as holding aircraft in the air or on the ground, to arrive or depart in the next hour.

The movement cap applies only to Sydney Airport. There is no limitation on the number of flights that can use other airports around Australia.