As long as you keep your sample in the fridge it will be good up to 5 days. Once you get to room temp from fridge (which takes about an hour) you are good to go to nuke in microwave for ONLY 10 seconds and stash immediately. As long as you keep them temp right, your sample will be fine for about 6-8 hours. I have done it before using frozen urine and it still passed lab tests.