How long is a tomato caterpillar in it's cacoon?

The Tomato Hornwarm's pupal stage is long and variable. We tried to keep some until they were moths, they made their cocoons under the dirt we put in the cage. Two years later they still hadn't come out so we thought they were dead. When we dumped out the cage in the woods we found them all (there were 3) in fully formed cocoons.