''Quickly it attaches to a substrate and encysts, as the reproducing stage. This life-stage doesn't eat. Its metabolic clock is now ticking; it is spending its stored energy to divide and divide again within the short-lived cyst. The tomont's time-span remains temperature-dependent: at common aquarium temperatures it's a matter of hours to days. (In a chilly koi pond in early spring, the cyst may persist longer.) Ultimately hundreds of mobile tomites burst from the cyst, even as many as 2000. They quick sprout cilia and start actively swimming about in search of a host. The fully developed "swarmers" are now called theronts (Greek ther- denotes a critter).''
Ich | The Skeptical Aquarist.
If you catch it in its free floating stage its extremely quick. I just cured a whole 75 gallon with malachite green and formalin- just about three days.