Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 17:15 and arrives at Jakarta Soekarno–Hatta International Airport at 20:55.
The flighttime is about 3h 40m. The distance travelled ("as the bird flies"): 830 Km. So the average speed is roughly 226 Km.
The best month to arrive at Bangkok is December and the most expensive month to fly is July. (Average prices, based on 407 datapoints.)
We have a lot more statistics for flights KL 869 and between Bangkok and Jakarta.