Do I need to be drinking a post-WOD Shake?
There are many variables and you must not overthink it. First and foremost, you need to focus on your goal and your overall calorie and macro consumption throughout the day. If you're getting this wrong, then trying to time your post workout anabolic window is meaningless!
If you are on top of your nutrition, CrossFit WODs generally use a high amount of glucose, the preferred fuel for high intensity or voluminous physical exertion. You should be focusing on replenishing your stores of carbohydrates if you want to be building muscle! Wait, I thought protein built muscle? Yes, it does, but carbs consumed immediately after training provide a powerful means of preventing muscle-loss through the secretion of insulin, a highly anabolic hormone.
In practical terms, post training, aim for a high carb, high protein drink for quick absorption with little fat. If there is any time in the day you are allowed to consume sugar, it's now!