If you see the SQ board, you will see that someone recently replied to me that the min check in time at KLIA is 40 mins.
I would say if you can pick up a boarding pass in SIN , then you are fine. Get off the plane and get back into the boarding lounge. Otherwise you have to get to a transfer desk within 10/15 mins of landing at KLIA than you should be OK.
Hopefully, you will not have checked in bags - in which case, no chance. Bags take forever to come out at KLIA unlike Changi.