Flight Incheon International Airport departs from Seoul Incheon International Airport at 12:40 and arrives at Tokyo Narita International Airport at 14:55.
The flighttime is about 2h 15m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 691 Km.
The best day to arrive at Seoul is Monday and it would be best to avoid Thursday, as prices are on average 86.12% higher than on Monday. (Average prices, based on 6774829 datapoints.)
We have a lot more statistics for flights OZ 104 and between Seoul and Tokyo.
