Flight Incheon International Airport departs from Seoul Incheon International Airport at 08:40 and arrives at Guangzhou Guangzhou Baiyun International Airport at 11:15.
The flighttime is about 3h 35m. The distance travelled ("as the bird flies"): 1648 Km. So the average speed is roughly 460 Km.
There is an 1 hour time difference between Seoul and Guangzhou