Flight Incheon International Airport departs from Seoul Incheon International Airport at 18:30 and arrives at Tokyo Haneda Airport at 21:00.
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 Friday and it would be best to avoid Tuesday, as prices are on average 289.67% higher than on Friday. (Average prices, based on 2492732 datapoints.)
We have a lot more statistics for flights NH 6978 and between Seoul and Tokyo.