I don't see why the hand warmer won't keep it warm enough. The temp should level off around 95-98 onced crotched. The only thing I have heard negative (which really isn't) is that the warmer can sometimes get the sample to hot. BUT....with a moment of swirling and blowing the temp will come back down ok. What I would do if I was you was to have a spare warmer (unopen) in your sock in case half way through the day you still haven't done your test. I personally think the one would do, but I tend to find ways to cover my a##. If at lunch you still haven't tested, pop open fresh warmer and apply (throw out older one).