When you remove bark really depends on what type of wood you're using. When using white woods like hickory, ash, elm, oak, maple, ect', You want to cut the wood while the sap is up and the bark peels easy. This will give you a flawless back for your bow without having to chase a ring. With other woods like osage, locust, mulberry, ect', where you use the heart wood and you have to chase a ring, it really doesn't matter when you peel the bark.
Another thing. With white wood, leaving the bark on too long will result in borers eating up the wood directly under the bark forcing you to chase a ring anyway. Hope this helps.