Flight Incheon International Airport departs from Seoul Incheon International Airport at 20:05 and arrives at Cebu Mactan-Cebu International Airport at 23:30.
The flighttime is about 4h 25m. The distance travelled ("as the bird flies"): 1750 Km. So the average speed is roughly 396 Km.
There is an 1 hour time difference between Seoul and Cebu