Flight Changi Airport departs from Singapore Changi Airport at 20:15 and arrives at Hong Kong Hong Kong International Airport at 00:10.
The flighttime is about 3h 55m. The distance travelled ("as the bird flies"): 1322 Km. So the average speed is roughly 338 Km.
The best day to arrive at Singapore is Wednesday and it would be best to avoid Friday, as prices are on average 41.75% higher than on Wednesday. (Average prices, based on 3159033 datapoints.)
We have a lot more statistics for flights CX 636 and between Singapore and Hong Kong.