Flight Gimpo International Airport departs from Seoul Gimpo International Airport at 20:30 and arrives at Jeju City International Airport at 21:40.
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 Wednesday and it would be best to avoid Saturday, as prices are on average 329.6% higher than on Wednesday. (Average prices, based on 437995 datapoints.)
We have a lot more statistics for flights 7C 141 and between Seoul and Jeju City.