You'll know that your cookies have finished cooking when they no longer look glossy on top and the edges look set. if you removed your baking sheet from the oven and gently push don't eh side of a cookie with your finger, the cookie shape shouldn't break, it should hold on to its circle and not become rippled like an accordion. Another great way to check is with an instant-read thermometer. The internal temperature of the cookies should read 165 degrees F.