Flight Gimpo International Airport departs from Seoul Gimpo International Airport at 07:45 and arrives at Tokyo Haneda Airport at 09:45.
The flighttime is about 2h 00m. The distance travelled ("as the bird flies"): 1450 Km. So the average speed is roughly 725 Km.
The best day to arrive at Seoul is Sunday and it would be best to avoid Tuesday, as prices are on average 55.93% higher than on Sunday. (Average prices, based on 1506667 datapoints.)
We have a lot more statistics for flights OZ 9128 and between Seoul and Tokyo.