Flight Changi Airport departs from Singapore Changi Airport at 10:20 and arrives at Koh Samui Samui International Airport at 11:05.
The flighttime is about 1h 45m. The distance travelled ("as the bird flies"): 475 Km. So the average speed is roughly 271 Km.
There is an 1 hour time difference between Singapore and Koh Samui