it is hard to go to sleep earlier than normal unless you are very tired and so it is unlikely you will fall asleep much earlier than normal and 

we assume that you need 4 hours before the flight to get up, travel to the airport and check-in, a reasonable assumption for international travel. If you need less time than that, then sleep as long as you can.  Unfortunately, the clash between your desired sleep pattern, shifting the clock and the flight times sometimes results in difficult requests. The long-term answer is to avoid early morning flights and either take an overnight flight and sleep, or a daytime flight at a time that permits a full sleep the night before leaving.