The longer knead times are necessary in some cases to develop the gluten.
5 minutes into kneading you will see the dough still has some texture issues.
The dough is more stiff and wraps around the hook.
After the 5 minutes you will start to notice that the dough gets more relaxed and starts to become smoother.
At work I allow a full 15 minutes to knead my sourdough baguette.