Flight Incheon International Airport departs from Seoul Incheon International Airport at 16:40 and arrives at Riyadh King Khaled International Airport at 21:40.
The flighttime is about 11h 00m. The distance travelled ("as the bird flies"): 8805 Km. So the average speed is roughly 800 Km.
There is an 6 hour time difference between Seoul and Riyadh