No, but I think it's best that way. If you want to make and eat the casserole in the same morning follow the same steps, but rather that letting it refrigerate overnight, just make sure to give it at least 30-60 minutes to soak up the custard. If you use this method, be sure to really press the bread cubes into the custard so that they're completely coated. You may also want to use a bread that is slightly softer or not as dried out.