I rotate between 3 or 4. When I swap them out, I break them down, and toss the bits in a water bottle with about 1/2" of rubbing alcohol. Each time I add something, I shake it. When I am down to one back up, I dump the alcohol, and rinse in the bottle by shaking in warm water 3 or 4 times.
Then, I rinse them individually as I take them out. Let dry, re-wick with boiled cotton, and they are good to go. With a few in rotation, the moment I taste anything burnt, or the first sign of a leak, I can swap it out. Sometimes this is every couple of days, sometimes a couple times in a day...
Heads are like razors... the first one you use gets replaced as soon as the first signs of dullness show, yet the last one can last for weeks if not months.