According to an article on ScienceDaily before-school activity programs have significant benefits for the physical fitness and social well-being of students. Unfortunately the article does not tell us what such program should like or whether different types of exercise could be used.
However, it seems that rope skipping is an excellent kind of exercise. According to this article on Time rope skipping is beneficial to virtually the entire body and hence one of the best fitness practices.
Since rope skipping is cheap and reasonably safe way of working out, we would argue that school children should start their day with between five and fifteen minutes of rope skipping.