Flight Tribhuvan International Airport departs from Kathmandu Tribhuvan International Airport at 19:20 and arrives at Seoul Incheon International Airport at 05:05.
The flighttime is about 6h 45m. The distance travelled ("as the bird flies"): 4562 Km. So the average speed is roughly 676 Km.
There is an 3 hour time difference between Kathmandu and Seoul