Not a dumb question at all, bro. A lot of guys use casein because of it's slower release. It's a much better choice than Whey iso, right before bed. Whey iso can be slowed down though with the use of fats in the shake. As long as it fits into your nutritional plan, I see no problem trying it. 

Do note that some people don't digest casein well. I am one of those people, so I just stay away from it. If you find that you experience abdominal bloating or gas, it may not be the best choice for you. If you have issue digesting nutrients, they aren't going to help you grow.