Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 23:05 and arrives at Jakarta Soekarno–Hatta International Airport at 02:40.
The flighttime is about 3h 35m. The distance travelled ("as the bird flies"): 830 Km. So the average speed is roughly 232 Km.
The best month to arrive at Bangkok is December and the most expensive month to fly is June. (Average prices, based on 716 datapoints.)
We have a lot more statistics for flights GA 8674 and between Bangkok and Jakarta.