Flight Changi Airport departs from Singapore Changi Airport at 01:50 and arrives at Tokyo Narita International Airport at 09:50.
The flighttime is about 7h 00m. The distance travelled ("as the bird flies"): 4385 Km. So the average speed is roughly 626 Km.
There is an 1 hour time difference between Singapore and Tokyo
The best day to arrive at Singapore is Friday and it would be best to avoid Sunday, as prices are on average 78.34% higher than on Friday. (Average prices, based on 488831 datapoints.)
We have a lot more statistics for flights JL 38 and between Singapore and Tokyo.