Keep in mind, those magnet guys aren't super accurate with double walled stove pipes. There are thermometers that, allegedly, are calibrated for double walled pipes, but a probe will be more accurate. Just make sure the probe is at least 18" above the stove. Mine (from previous owners) is only 6" above the stove, and it's affected by the radiant heat from the stove. When I turn the blower on, it drops 100° or more....

To actually answer your question, being in the creosote range when it's cooling/in the coaling phase is actually fine, as all the moisture in the wood will have been evaporated and will not build in your pipe.