I have been in the practice of staying at SIN (airside) after late night arrival until about 6 am (eg 11ish to 6 am). Never had a problem - BUT I just remembered that the last time I was there some policeman stopped and asked to see my onward ticket. They said there is a new regulation that you cannot stay airside for more than 3 hours after arrival w/o an onward ticket. Does anyone know if this is (still) true?