Flight Narita International Airport departs from Tokyo Narita International Airport at 09:00 and arrives at Seoul Incheon International Airport at 11:35.
The flighttime is about 2h 35m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 602 Km.
The best day to arrive at Tokyo is Saturday and it would be best to avoid Friday, as prices are on average 120.99% higher than on Saturday. (Average prices, based on 4214268 datapoints.)
We have a lot more statistics for flights OZ 107 and between Tokyo and Seoul.