Flight Incheon International Airport departs from Seoul Incheon International Airport at 22:40 and arrives at Tokyo Haneda Airport at 00:50.
The flighttime is about 2h 10m. The distance travelled ("as the bird flies"): 1487 Km. So the average speed is roughly 686 Km.
The best day to arrive at Seoul is Tuesday and it would be best to avoid Monday, as prices are on average 137.44% higher than on Tuesday. (Average prices, based on 2643356 datapoints.)
We have a lot more statistics for flights MM 808 and between Seoul and Tokyo.
