Please be aware that Seoul and Osaka has multiple airports and that these results are for all airports serving the city.
The best month to fly between Seoul and Osaka is January and the most expensive month to fly is March. (Average prices, based on 209 datapoints.)
The best day to arrive at Seoul is Saturday and it would be best to avoid Thursday, as prices are on average 87.71% higher than on Saturday. (Average prices, based on 351 datapoints.)
The best time to fly is at around 11. (Average prices, based on 322 datapoints.)