Flight Don Mueang International Airport departs from Bangkok Don Mueang International Airport at 02:45 and arrives at Kaohsiung International Airport at 07:15.
The flighttime is about 3h 30m. The distance travelled ("as the bird flies"): 2215 Km. So the average speed is roughly 633 Km.
There is an 1 hour time difference between Bangkok and Kaohsiung