Their major drawback was the time they took to prepare and put on. Typically, it would take Lirael five hours or more to prepare a charter skin, another hour to fold it properly so that it would last a day or two in a pouch or bag, and then at least half an hour to put on. Sometimes it took longer, particularly the ice-otter skin, because it was so much smaller than Lirael's normal form.

Lirael, Ch. 20, pg. 180