If the Japanese continue their (OTL successful) invasions of the DEI then Singapore is unsupportable and falls some months later.
But...
If it repels the initial invasion, will the Japanese be able to move some of the troops to invade Burma? With a strong garrison in Singapore that acts aggressively? With Singapore holding, it seems unlikely (the Japanese invasion was working on a shoestring). Given a few more months, its quite possible Japan gets held in Burma, which will have big implications.
How long Singapore can hold would depend on how much air power Japan devotes to stopping any convoys. They certainly have the ability to do so. But this probably means no Indian Ocean raid, again giving the RN more time to regroup and prepare. If the garrison can hold until Midway, it might be interesting. But once Sumatra falls Singapore is untenable in the long run.