Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 02:15 and arrives at Kolkata Netaji Subhas Chandra Bose International Airport at 03:25.
The flighttime is about 2h 40m. The distance travelled ("as the bird flies"): 1366 Km. So the average speed is roughly 512 Km.
There is an 1.5 hour time difference between Bangkok and Kolkata