Flight Narita International Airport departs from Tokyo Narita International Airport at 18:55 and arrives at Seoul Incheon International Airport at 21:50.
The flighttime is about 2h 55m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 533 Km.
The best day to arrive at Tokyo is Wednesday and it would be best to avoid Sunday, as prices are on average 241.23% higher than on Wednesday. (Average prices, based on 4216462 datapoints.)
We have a lot more statistics for flights TW 216 and between Tokyo and Seoul.