Flight Incheon International Airport departs from Seoul Incheon International Airport at 09:55 and arrives at Tokyo Narita International Airport at 12:20.
The flighttime is about 2h 25m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 643 Km.
The best day to arrive at Seoul is Saturday and it would be best to avoid Tuesday, as prices are on average 425.13% higher than on Saturday. (Average prices, based on 6777170 datapoints.)
We have a lot more statistics for flights AM 6750 and between Seoul and Tokyo.