Flight Soekarno–Hatta International Airport departs from Jakarta Soekarno–Hatta International Airport at 15:00 and arrives at Semarang Achmad Yani International Airport at 16:10.
The flighttime is about 1h 10m. The distance travelled ("as the bird flies"): 415 Km. So the average speed is roughly 356 Km.
The best day to arrive at Jakarta is Saturday and it would be best to avoid Thursday, as prices are on average 45.8% higher than on Saturday. (Average prices, based on 130894003 datapoints.)
We have a lot more statistics for flights GA 2424 and between Jakarta and Semarang.