Flight Haneda Airport departs from Tokyo Haneda Airport at 22:55 and arrives at Singapore Changi Airport at 05:15.
The flighttime is about 7h 20m. The distance travelled ("as the bird flies"): 4314 Km. So the average speed is roughly 588 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 Friday, as prices are on average 304.19% higher than on Sunday. (Average prices, based on 495868 datapoints.)
We have a lot more statistics for flights NH 6251 and between Tokyo and Singapore.