How long does it take for a catapiller to change into it's cacoon?

The transformation of a caterpillar into a chrysalis (often referred to as a cocoon, although technically that term is used for silk structures made by some species) typically occurs after the caterpillar has fully matured and eaten enough food. This process, called pupation, can take a few hours to a couple of days, depending on the species and environmental conditions. Once inside the chrysalis, the caterpillar undergoes metamorphosis and will emerge as a butterfly or moth after several days to weeks.