It sounds like they just peed and didn't groom themselves yet. They just woke up?
However, if you are at all concerned, you should go to a vet! Anything that is not "normal" to your gliders - whether or not it is normal for someone else's - should be checked out by your vet.
I would hesitantly suggest that it can wait until tomorrow? I don't really know - but it doesn't sound immediately life threatening.
Don't forget, taking them to the vet for this kind of check is a great opportunity to run a fecal!