Well, we need more info, but I'd say in that amount of time it was already on its way out. Did you take it straight home and acclimate it? What did it look like when purchased?
Ya, give it over night unless he is just turning to "wet toilet paper" in your tank. They can shed and slime. But if you notice tissue just falling off of him, you might want to chunk him. Do you have water in your QT?!? I would put him in there.