Flight Haneda Airport departs from Tokyo Haneda Airport at 02:05 and arrives at Singapore Changi Airport at 08:20.
The flighttime is about 7h 15m. The distance travelled ("as the bird flies"): 4314 Km. So the average speed is roughly 595 Km.
There is an 1 hour time difference between Tokyo and Singapore
The best day to arrive at Tokyo is Sunday and it would be best to avoid Tuesday, as prices are on average 138.15% higher than on Sunday. (Average prices, based on 491152 datapoints.)
We have a lot more statistics for flights SQ 639 and between Tokyo and Singapore.