Flight Changi Airport departs from Singapore Changi Airport at 08:50 and arrives at Colombo Bandaranaike International Airport at 10:05.
The flighttime is about 3h 45m. The distance travelled ("as the bird flies"): 2677 Km. So the average speed is roughly 714 Km.
There is an 2.5 hour time difference between Singapore and Colombo