Flight Narita International Airport departs from Tokyo Narita International Airport at 19:25 and arrives at Seoul Incheon International Airport at 22:20.
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 Thursday and it would be best to avoid Friday, as prices are on average 248.46% higher than on Thursday. (Average prices, based on 4215861 datapoints.)
We have a lot more statistics for flights OZ 105 and between Tokyo and Seoul.