Flight Haneda Airport departs from Tokyo Haneda Airport at 15:45 and arrives at Seoul Incheon International Airport at 18:20.
The flighttime is about 2h 35m. The distance travelled ("as the bird flies"): 1487 Km. So the average speed is roughly 576 Km.
The best day to arrive at Tokyo is Tuesday and it would be best to avoid Thursday, as prices are on average 45.21% higher than on Tuesday. (Average prices, based on 1485669 datapoints.)
We have a lot more statistics for flights KE 5710 and between Tokyo and Seoul.
