Flight Gimpo International Airport departs from Seoul Gimpo International Airport at 19:20 and arrives at Jeju City International Airport at 20:35.
The flighttime is about 1h 15m. The distance travelled ("as the bird flies"): 271 Km. So the average speed is roughly 217 Km.
The best day to arrive at Seoul is Wednesday and it would be best to avoid Tuesday, as prices are on average 892.8% higher than on Wednesday. (Average prices, based on 438005 datapoints.)
We have a lot more statistics for flights OZ 8991 and between Seoul and Jeju City.