No I leave em in for months. If it works it works. If you get to six months treat yourself to a new one.I can't bring myself to change it cause it works, the next one might be crap.
As the title says, bought a Kayfun v3 mini beginning of April, put a coil on it and have had it in there ever since (obviously re-wicked every week or two). It works a treat but should I be changing it (bearing in mind I am very lazy!).