Flight Incheon International Airport departs from Seoul Incheon International Airport at 15:45 and arrives at Tokyo Haneda Airport at 18:15.
The flighttime is about 2h 30m. The distance travelled ("as the bird flies"): 1487 Km. So the average speed is roughly 595 Km.
The best day to arrive at Seoul is Thursday and it would be best to avoid Tuesday, as prices are on average 85.23% higher than on Thursday. (Average prices, based on 2456771 datapoints.)
We have a lot more statistics for flights NH 6976 and between Seoul and Tokyo.