The workouts in your first training weeks take into account your initial level. In order to get better, you need to build up the intensity and duration of your training sessions gradually. That's why the first workouts tend to be on the shorter side.
This will be extended over time when we see that you are indeed improving (you will be!) and the training plan evolves. The same applies when we judge it prudent to take the foot off the gas a little bit and give you an easier week to allow for some recovery after a few hard weeks. In that case, you will likely get a few workouts that are shorter than the availability that you have indicated.