Flight Gimpo International Airport departs from Seoul Gimpo International Airport at 09:00 and arrives at Tokyo Haneda 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 month to arrive at Seoul is March and the most expensive month to fly is July. (Average prices, based on 857 datapoints.)
The best day to arrive at Seoul is Sunday and it would be best to avoid Tuesday, as prices are on average 53.72% higher than on Sunday. (Average prices, based on 1126781 datapoints.)
We have a lot more statistics for flights JL 5234 and between Seoul and Tokyo.