Flight Noi Bai International Airport departs from Hanoi Noi Bai International Airport at 23:35 and arrives at Seoul Incheon International Airport at 05:50.
The flighttime is about 4h 15m. The distance travelled ("as the bird flies"): 2409 Km. So the average speed is roughly 567 Km.
There is an 2 hour time difference between Hanoi and Seoul