Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 21:00 and arrives at Bandar Seri Begawan Brunei International Airport at 00:45.
The flighttime is about 2h 45m. The distance travelled ("as the bird flies"): 1600 Km. So the average speed is roughly 582 Km.
There is an 1 hour time difference between Bangkok and Bandar Seri Begawan