Flight Soekarno–Hatta International Airport departs from Jakarta Soekarno–Hatta International Airport at 16:00 and arrives at Medan Kualanamu International Airport at 18:30.
The flighttime is about 2h 30m. The distance travelled ("as the bird flies"): 895 Km. So the average speed is roughly 358 Km.
The best month to arrive at Jakarta is February and the most expensive month to fly is December. (Average prices, based on 4245 datapoints.)
We have a lot more statistics for flights SQ 180 and between Jakarta and Medan.