Flight Changi Airport departs from Singapore Changi Airport at 08:10 and arrives at Koh Samui Samui International Airport at 09:05.
The flighttime is about 1h 55m. The distance travelled ("as the bird flies"): 475 Km. So the average speed is roughly 248 Km.
There is an 1 hour time difference between Singapore and Koh Samui