Flight Narita International Airport departs from Tokyo Narita International Airport at 18:55 and arrives at Seoul Incheon International Airport at 21:45.
The flighttime is about 2h 50m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 549 Km.
The best day to arrive at Tokyo is Tuesday and it would be best to avoid Friday, as prices are on average 879.64% higher than on Tuesday. (Average prices, based on 4526673 datapoints.)
We have a lot more statistics for flights TW 246 and between Tokyo and Seoul.
