Flight Incheon International Airport departs from Seoul Incheon International Airport at 12:15 and arrives at Tokyo Haneda Airport at 14:40.
The flighttime is about 2h 25m. The distance travelled ("as the bird flies"): 1487 Km. So the average speed is roughly 615 Km.
The best day to arrive at Seoul is Thursday and it would be best to avoid Tuesday, as prices are on average 45.56% higher than on Thursday. (Average prices, based on 2456937 datapoints.)
We have a lot more statistics for flights OZ 104 and between Seoul and Tokyo.