Flight Incheon International Airport departs from Seoul Incheon International Airport at 20:00 and arrives at Hong Kong Hong Kong International Airport at 16:15.The flight has a short stop at Shanghai.
The flighttime is about 21h 15m. The distance travelled ("as the bird flies"): 1621 Km. So the average speed is roughly 76 Km.
There is an 1 hour time difference between Seoul and Hong Kong