Flight Incheon International Airport departs from Seoul Incheon International Airport at 15:45 and arrives at Tokyo Narita International Airport at 18:25.
The flighttime is about 2h 40m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 583 Km.
The best day to arrive at Seoul is Thursday and it would be best to avoid Tuesday, as prices are on average 40.04% higher than on Thursday. (Average prices, based on 6935920 datapoints.)
We have a lot more statistics for flights OZ 106 and between Seoul and Tokyo.