Flight Chiang Mai International Airport departs from Chiang Mai Chiang Mai International Airport at 20:40 and arrives at Seoul Incheon International Airport at 04:00.
The flighttime is about 5h 20m. The distance travelled ("as the bird flies"): 3123 Km. So the average speed is roughly 586 Km.
There is an 2 hour time difference between Chiang Mai and Seoul