Ideally, you will have a nicely rounded, smooth top of your bread once it is baked. But if it is sagging and wrinkly it is because you let it rise for too long. I find that somewhere in the 18-20 minute range is perfect in my home. But based on your house temperature, it may be different for you. Keep an eye on it and place it in your preheated oven once it has doubled in size.