Flight Incheon International Airport departs from Seoul Incheon International Airport at 07:15 and arrives at Tokyo Narita International Airport at 10:10.
The flighttime is about 2h 55m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 533 Km.
The best day to arrive at Seoul is Tuesday and it would be best to avoid Sunday, as prices are on average 230.07% higher than on Tuesday. (Average prices, based on 6739675 datapoints.)
We have a lot more statistics for flights ZE 605 and between Seoul and Tokyo.