This is from the SINGAPORE AOC regulations pertaining to FDP:
The maximum permitted (rostered) Flight Duty Period may be extended when the Normal Flight Crew complement is augmented with Augmented Flight Crew according to the following:
a) Up to a maximum FDP of 15 hours if augmented with one flight crew (each flight crew member can leave their assigned post and be replaced by another appropriately qualified flight crew member for the purpose of in-flight rest) and appropriate rest facilities are available for one pilot.
b) Up to a maximum FDP of 18 hours if augmented with two flight crew (each flight crew member can leave their assigned post and be replaced by another appropriately qualified flight crew member for the purpose of in-flight rest) and appropriate rest facilities are available for two pilots.
Bear in mind that the Regulator also allows a maximum of 3 hours duty extension (at commander's discretion).