12 to 15 minutes is how long it takes to bake most cookies.
To soften hard cookies you can put the hard cookies into an airtight container with some moist bread or even a damp paper towel and the cookies should begin softening.
Another way to soften hard cookies is to put some water in the oven and allow the steam from the water to warm up and soften the cookies.
Or simply dipping the cookies in some milk or coffee can help to soften the cookies as well.
The most common reason cookies turn out hard after baking them is because you overworked the dough.
When you overwork the dough the dough becomes harder and harder the longer you work and knead the dough.
Flour contains gluten which is a protein that gets tougher and harder the more you knead, roll and mix it so you don't want to work or knead, roll or mix the dough too long.
Over baking the cookies is another reason some cookies turn out hard.
You want to work the dough just long enough to mix it together but not long enough to make the dough too hard.
When you bake the cookies you should bake them until they are soft and firm but not too firm or hard.
When baking cookies you bake the cookies at 350 F to 375 F and bake the cookies for 12 to 15 minutes.
After 12 minutes in the oven you can check to see if the cookies are done and still soft.
I bake my cookies for 12 minutes which is enough to cook the cookies but not cook them to be too hard.