I transit through Changi arriving at midnight and leaving at around 6am. I arrive business class on UA and leave economy on a non-Star Alliance airline. I don't have status on Star Alliance at this point.

Question: Is there any lounge open at that hour that will let me in with an UA arrival business boarding card?

I realize that I could go to the transit hotel but it is usually hard to get a reservation there. Thanks for any info you may have.