Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 23:15 and arrives at Tokyo Narita International Airport at 06:55.
The flighttime is about 5h 40m. The distance travelled ("as the bird flies"): 4511 Km. So the average speed is roughly 796 Km.
There is an 2 hour time difference between Bangkok and Tokyo
The best day to arrive at Bangkok is Saturday and it would be best to avoid Tuesday, as prices are on average 252.64% higher than on Saturday. (Average prices, based on 613618 datapoints.)
We have a lot more statistics for flights NH 5598 and between Bangkok and Tokyo.