The heat pack that comes with the QF takes approximately 1 hour to heat a 'cold' bottle of QF to 100 degrees. From experience, when the bottle was mic'd first, then the heat pack attached, the heat pack got hot sooner.

If you get hit with a random with no access to any heat source besides the heat pack, go ahead and go to the clinic. Fill out all the paperwork and take the sample cup to the bathroom. Use this time to activate the heatpack and attach it to the QF bottle (you did remember to keep a rubberband handy, did you?). Then walk out of the bathroom and tell the tech that you cannot pee right now. The tech will then instruct you to sit in the lobby and "drink some water until you can pee". The tech has to give you 3 hours to produce an adequate amount of sample before ruling it a 'refusal to test'. Thats more than plenty of time for the heat pack to get hot. Take an hour of those three to play along with the gag by drinking water until the QF bottle gets up to temp.