Splitting an hour into tiny chunks and forcing yourself to follow fixed amounts of minutes on each topic is wasting your time.
With only an hour, I choose one topic (which doesn't mean a single exercise) and just focus on that. If I really feel I practiced enough before the end of the hour, or if otherwise I am not really getting into the topic at all, maybe a choose a second topic.
In no case I stop an exercise after a predetermined amounts of minutes. I stop when I get the feeling I have been doing the exercise well and long enough so that something remains.
With only an hour, I choose one topic (which doesn't mean a single exercise) and just focus on that. If I really feel I practiced enough before the end of the hour, or if otherwise I am not really getting into the topic at all, maybe a choose a second topic.
In no case I stop an exercise after a predetermined amounts of minutes. I stop when I get the feeling I have been doing the exercise well and long enough so that something remains.