Flight Narita International Airport departs from Tokyo Narita International Airport at 09:00 and arrives at Seoul Incheon International Airport at 11:30.
The flighttime is about 2h 30m. The distance travelled ("as the bird flies"): 1555 Km. So the average speed is roughly 622 Km.
The best day to arrive at Tokyo is Sunday and it would be best to avoid Saturday, as prices are on average 171.95% higher than on Sunday. (Average prices, based on 4539542 datapoints.)
We have a lot more statistics for flights OZ 107 and between Tokyo and Seoul.
