Flight Noi Bai International Airport departs from Hanoi Noi Bai International Airport at 01:05 and arrives at Busan Gimhae International Airport at 07:05.
The flighttime is about 4h 00m. The distance travelled ("as the bird flies"): 2654 Km. So the average speed is roughly 664 Km.
There is an 2 hour time difference between Hanoi and Busan