Flight Gimhae International Airport departs from Busan Gimhae International Airport at 21:35 and arrives at Hong Kong Hong Kong International Airport at 00:05.
The flighttime is about 3h 30m. The distance travelled ("as the bird flies"): 1822 Km. So the average speed is roughly 521 Km.
There is an 1 hour time difference between Busan and Hong Kong