I wouldn't bother with the heat pad unless you put the QF in your pocket. If you nuke the QF for 10 seconds and then put it in your crotch it will be good for a couple hours unless your outside a lot in cold weather, The heat pad is for backup in case the temp gets low.
If when you take the UA and your temp is a little low,rub your thumb briskly on your clothing and then hold your thumb against the temp strip on the cup for a few seconds.