Flight Narita International Airport departs from Tokyo Narita International Airport at 11:45 and arrives at Bandar Seri Begawan Brunei International Airport at 16:45.
The flighttime is about 6h 00m. The distance travelled ("as the bird flies"): 3449 Km. So the average speed is roughly 575 Km.
There is an 1 hour time difference between Tokyo and Bandar Seri Begawan