Once it is preheated, place the baking tray in the oven and start baking, It took exactly 10 mins to bake the cookies at the right amount of crispness. The time varies according to the oven. If you are trying cookies for the first time, check often. When it is hot, it will be slightly soft, allow them to cool down for a while, then it becomes firm and crispy. Do not wait for the cookie to get firm while baking, it will become harder once it is cool down. If you make one batch, you will get the idea about the timing.