Flight Incheon International Airport departs from Seoul Incheon International Airport at 18:40 and arrives at Phnom Penh Phnom Penh International Airport at 22:10.
The flighttime is about 5h 30m. The distance travelled ("as the bird flies"): 2655 Km. So the average speed is roughly 483 Km.
There is an 2 hour time difference between Seoul and Phnom Penh