Flight Changi Airport departs from Singapore Changi Airport at 19:15 and arrives at Perth Perth Airport at 00:25.
The flighttime is about 5h 10m. The distance travelled ("as the bird flies"): 1789 Km. So the average speed is roughly 346 Km.
The best day to arrive at Singapore is Tuesday and it would be best to avoid Wednesday, as prices are on average 130.45% higher than on Tuesday. (Average prices, based on 275348 datapoints.)
We have a lot more statistics for flights QF 72 and between Singapore and Perth.