I had just taken a DOT test last Wednesday using real piss collected on the Friday b-4. I kept it in a good airtight bottle in the 'fridge, and took it out in the morning of the test, put it in my 2oz bottles, which have a temp strip [reusing bottle from p-sure...a brand of synthetic urine]. Right b-4 I left for the test [which is 20 minute's away], I nuked it a couple of time's at 10 second's, untill I had a 100 degree reading. I had misplaced my digatel thermomater, so I relied on the temp strips. I kept the bottle next to my inner thigh, and nut sack, using a jock, and tighty whitie's. My temp was acceptable, I practiced this method, and after 1/2 hour I was still good. I myself, would be concerned with your time-frame, and use a heating pad, just to be sure. Also have you read the subbing sticky on top of this page? Excellent info! Hope this help's. Good luck!