Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 03:15 and arrives at Guangzhou Guangzhou Baiyun International Airport at 07:50.
The flighttime is about 3h 35m. The distance travelled ("as the bird flies"): 1426 Km. So the average speed is roughly 398 Km.
There is an 1 hour time difference between Bangkok and Guangzhou