Please be aware that Seoul has multiple airports and that these results are for all airports serving the city.
The best month to fly between Seoul and Busan is May and the most expensive month to fly is September. (Average prices, based on 1262 datapoints.)
The best day to arrive at Seoul is Monday and it would be best to avoid Friday, as prices are on average 61.24% higher than on Monday. (Average prices, based on 221 datapoints.)
The best time to fly is at around 6. (Average prices, based on 1354 datapoints.)