Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 00:20 and arrives at Hong Kong Hong Kong International Airport at 04:30.
The flighttime is about 3h 10m. The distance travelled ("as the bird flies"): 1487 Km. So the average speed is roughly 470 Km.
There is an 1 hour time difference between Bangkok and Hong Kong
