I wouldn't store it more than 6 hours, urine begins to go bad after 8 hours. If you can collect the sample an hour or two before you go it would be best. The hand warmer will keep the temperature at around 100 degrees for 5-6 hours. The acceptable temperature range is between 90-100 degrees. I would try to get it around 96- 98 if you can so you don't look suspicious.