Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 23:50 and arrives at Tokyo Narita International Airport at 08:10.
The flighttime is about 6h 20m. The distance travelled ("as the bird flies"): 4511 Km. So the average speed is roughly 712 Km.
There is an 2 hour time difference between Bangkok and Tokyo
The best day to arrive at Bangkok is Monday and it would be best to avoid Sunday, as prices are on average 86.78% higher than on Monday. (Average prices, based on 452312 datapoints.)
We have a lot more statistics for flights TG 642 and between Bangkok and Tokyo.