Flight Narita International Airport departs from Tokyo Narita International Airport at 11:45 and arrives at Bangkok Suvarnabhumi Airport at 17:05.
The flighttime is about 7h 20m. The distance travelled ("as the bird flies"): 4511 Km. So the average speed is roughly 615 Km.
There is an 2 hour time difference between Tokyo and Bangkok
The best day to arrive at Tokyo is Sunday and it would be best to avoid Thursday, as prices are on average 133.7% higher than on Sunday. (Average prices, based on 163162 datapoints.)
We have a lot more statistics for flights TG 643 and between Tokyo and Bangkok.