Flight Incheon International Airport departs from Seoul Incheon International Airport at 21:30 and arrives at Tokyo Haneda Airport at 23:25.
The flighttime is about 1h 55m. The distance travelled ("as the bird flies"): 1487 Km. So the average speed is roughly 776 Km.
The best day to arrive at Seoul is Sunday and it would be best to avoid Thursday, as prices are on average 105.24% higher than on Sunday. (Average prices, based on 2655744 datapoints.)
We have a lot more statistics for flights OZ 178 and between Seoul and Tokyo.
