In Southern Canada the Cercropia moth imerges from it's cocoon around the first or second week in June. The exact pupate time depends on your location. It's quite the wait but well worth it. Keep the cocoon in a well vented mouse-proof container outside in a sheltered place, like a shed or unheated garage. You don't want the pupa to dehydrate in a heated or A/C enviroment and you also do not want to speed up it's developement or it will be the only Cercropia around when you let it free and it will not be able to find a mate.
Make sure you have a camera ready.