"Is there a window for putting on size?"

Your body is a beautiful instrument.

Food fuels it. Without food,the body begins to go into a "state of emergency" where it begins to eat off the nutrients already consumed inside. In the fitness world,there's alot of narratives. If you workout on an empty stomach,it is imperative that you feed the body as soon as possible to stimulate growth. If you do have a meal,it should be the same. However,there are some who say different. But if you're trying to grow(same theory for anything), you should invest in it,which in this case feed yourself the proper nutrition for your goal(s).