Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 13:45 and arrives at Guangzhou Guangzhou Baiyun International Airport at 18:15.
The flighttime is about 3h 30m. The distance travelled ("as the bird flies"): 1426 Km. So the average speed is roughly 407 Km.
There is an 1 hour time difference between Bangkok and Guangzhou