How long does it take to outgrow crosseyes?

Never: By outgrow i’m assuming childhood disease. Esotropia or in-crossed eyes have critical ages for straightening either with glasses or surgery. If less than 2 years old: very critical. Age 2-4 asap. After age 4 getting 3d vision becomes rarer even after surgery. 3d vision keeps eyes straight. Exo deviations or out-crossing of eyes can be treated with glasses or prisms sometimes but may need surgery.

You don't: A newborn may transiently cross his/her eyes, especially when tired.However after a few months, the tracking reflex/with both eyes following the same object & pointing in the same direction is firmly established. Untreated, the issue will be permanent.