Flight Narita International Airport departs from Tokyo Narita International Airport at 19:00 and arrives at Seoul Incheon International Airport at 21:40.
The flighttime is about 2h 40m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 583 Km.
The best day to arrive at Tokyo is Wednesday and it would be best to avoid Sunday, as prices are on average 456.97% higher than on Wednesday. (Average prices, based on 4309905 datapoints.)
We have a lot more statistics for flights LJ 208 and between Tokyo and Seoul.
