Flight Haneda Airport departs from Tokyo Haneda Airport at 08:40 and arrives at Seoul Incheon International Airport at 11:15.
The flighttime is about 2h 35m. The distance travelled ("as the bird flies"): 1487 Km. So the average speed is roughly 576 Km.
The best day to arrive at Tokyo is Monday and it would be best to avoid Sunday, as prices are on average 78.6% higher than on Monday. (Average prices, based on 1607691 datapoints.)
We have a lot more statistics for flights OZ 1055 and between Tokyo and Seoul.
