Flight Kualanamu International Airport departs from Medan Kualanamu International Airport at 16:45 and arrives at Jakarta Soekarno–Hatta International Airport at 19:15.
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 Medan is February and the most expensive month to fly is January. (Average prices, based on 3437 datapoints.)
We have a lot more statistics for flights KE 121 and between Medan and Jakarta.