If they do it this way, they are doing it wrong.
At my current job I can squeeze all my daily tasks in maybe one hour (mind you, this is after 10 years of doing a very similar set of things). It becomes longer when a significant change comes or an emergency happens but after a few weeks it's all the same. I study new things and develop my competences during the spare hours but I can imagine I could earn money as well. The pay is good so I don't have motivation to take an extra job but I can totally understand people who are more ambitious or earn less.