the hand warmers you are using start heating to their max temp as soon as you open the package. they usually reach the max temp in about 10 minutes or so. but be careful, some of them have a max temp upwards of 140 degrees! check the back of the pacage to see what yours does. most of them will hold the temp for about 5 hours.

Actually ,the heat packs that come with the QF take approximately 1 hour to heat a QF bottle (that was stored at room temp)to 100 F. Thats why its recommended that the QF bottle should be preheated (via mic, hot water, etc) before banding the heat pack to it.

In the several years that Ive used the QF, Ive never encountered problems with the heat pack overheating the bottle. :thumbsup: