Flight Changi Airport departs from Singapore Changi Airport at 20:10 and arrives at Hong Kong Hong Kong International Airport at 00:25.
The flighttime is about 4h 15m. The distance travelled ("as the bird flies"): 1322 Km. So the average speed is roughly 311 Km.
The best day to arrive at Singapore is Wednesday and it would be best to avoid Friday, as prices are on average 43.13% higher than on Wednesday. (Average prices, based on 2263973 datapoints.)
We have a lot more statistics for flights CX 636 and between Singapore and Hong Kong.