Flight Incheon International Airport departs from Seoul Incheon International Airport at 14:50 and arrives at Guangzhou Guangzhou Baiyun International Airport at 17:55.
The flighttime is about 4h 05m. The distance travelled ("as the bird flies"): 1648 Km. So the average speed is roughly 404 Km.
There is an 1 hour time difference between Seoul and Guangzhou
