Let's said that they are sent 1 month earlier and safely reach Singapore before the start of the war, what are they going to do? Even if PoW is a very modern ship, without any additional ships it would be suicidal to try to contest the sea domination to the Japanese. Would they be able to act as naval artillery and for instance decisively help the defender to beat Yamashita's first wave and hence hold for a few more weaks/month?