The OP does mention that long hours are not sustainable which recognizes that occasional bursts of extra effort will get results. As for point number 5, nobody said that people should go home and sleep at the end of their 8 hour day. If you have a hobby that is completely different from your day job, then it will energize you, as you have discovered. Your day job is management and your hobby is coding.
Most of my hobbies are related to my product - so no issues there. But even in the main project, there are some issues that require the personal attention of senior engineers. These will require time aside from the regular co-ordination / mentoring.
Also I don't manage people. Just projects - a Technical lead so to say.
