Assuming you are referring to the dessert, the answer is technically yes, they can be left out. Oreo truffles are made with Oreo cookies, cream cheese and chocolate, and these are all ingredients that are safe to leave out at room temperature. However, the quality of the truffles will suffer if they are left out for too long. The cream cheese will start to sweat and the truffles will become mushy. If you want your Oreo truffles to taste their best, it is best to store them in the fridge.