Flight Haneda Airport departs from Tokyo Haneda Airport at 09:00 and arrives at Seoul Gimpo International Airport at 11:20.
The flighttime is about 2h 20m. The distance travelled ("as the bird flies"): 1450 Km. So the average speed is roughly 621 Km.
The best day to arrive at Tokyo is Tuesday and it would be best to avoid Sunday, as prices are on average 161.67% higher than on Tuesday. (Average prices, based on 391567 datapoints.)
We have a lot more statistics for flights OZ 1055 and between Tokyo and Seoul.