Flight Pudong International Airport departs from Shanghai Pudong International Airport at 23:55 and arrives at Siem Reap Siem Reap-Angkor International Airport at 03:15.
The flighttime is about 4h 20m. The distance travelled ("as the bird flies"): 2120 Km. So the average speed is roughly 489 Km.
There is an 1 hour time difference between Shanghai and Siem Reap