Flight Changi Airport departs from Singapore Changi Airport at 11:00 and arrives at Seoul Incheon International Airport at 18:40.
The flighttime is about 6h 40m. The distance travelled ("as the bird flies"): 2923 Km. So the average speed is roughly 438 Km.
There is an 1 hour time difference between Singapore and Seoul
The best day to arrive at Singapore is Thursday and it would be best to avoid Friday, as prices are on average 76.42% higher than on Thursday. (Average prices, based on 663863 datapoints.)
We have a lot more statistics for flights KE 648 and between Singapore and Seoul.