Flight Chiang Mai International Airport departs from Chiang Mai Chiang Mai International Airport at 21:20 and arrives at Seoul Incheon International Airport at 04:30.
The flighttime is about 5h 10m. The distance travelled ("as the bird flies"): 3123 Km. So the average speed is roughly 604 Km.
There is an 2 hour time difference between Chiang Mai and Seoul