The mental skills are equally unfamiliar, and that adjustment takes time, too. As you grow accustomed to procedure, you can extend your meditation little by little. We recommend that after a year or so of steady practice you should be sitting comfortable for an hour at a time. Self-mortification is not the goal. We are trying to cultivate mindfulness, not pain.
Some pain is inevitable, especially in the legs.
We will thoroughly cover pain, and how to handle it, in Chapter 10. There are special techniques and attitudes which you will learn for dealing with discomfort. You don't need to prove anything to anybody. So don't force yourself to sit with excruciating pain just to be able to say that you sat for an hour. That is a useless exercise in ego.