Old Fashioned Oats and Quick Oats differ in the way they have been prepared. Old Fashioned Oats are a flattened grain, they hold their firm texture, and they cook in about 5-10 minutes. Quick Oats are a thinner grain, they're softer and can cook in 1 minute. In most cases, these types of oats are interchangeable. However, if you use quick oats in these cookies, you may find that the result is chewier or gummier than intended, and have more of an oat taste to them.