Killer, you ask a question that I still have no scientific answer for. I do know from my own experments that after 8 hours the smell is RANK!, and at 24-48 hours stuff will start to grow on top of the sample. As for an air tight container, all I can say is if you keep meat or mayo at room temp for 8 hours, reguardless of the type container, you risk serious food poisening. I would guess that after 8 hours that the bacteria level in the urine may effect the pH and creatinine levels. So I simply repeate what folk in the urine selling business tell me. But please, feel free to call a few urine vendors yourself, ask them and report back to the board. N2