Flight Haneda Airport departs from Tokyo Haneda Airport at 20:05 and arrives at Seoul Gimpo International Airport at 22:35.
The flighttime is about 2h 30m. The distance travelled ("as the bird flies"): 1450 Km. So the average speed is roughly 580 Km.
The best day to arrive at Tokyo is Sunday and it would be best to avoid Tuesday, as prices are on average 177.13% higher than on Sunday. (Average prices, based on 398438 datapoints.)
We have a lot more statistics for flights NH 6969 and between Tokyo and Seoul.