Flight Gimpo International Airport departs from Seoul Gimpo International Airport at 07:15 and arrives at Jeju City International Airport at 08:25.
The flighttime is about 1h 10m. The distance travelled ("as the bird flies"): 271 Km. So the average speed is roughly 232 Km.
The best day to arrive at Seoul is Saturday and it would be best to avoid Tuesday, as prices are on average 615.79% higher than on Saturday. (Average prices, based on 442161 datapoints.)
We have a lot more statistics for flights KE 1019 and between Seoul and Jeju City.