I really hope you don't start a company and have people work on the weekends and threaten them with their job if they refuse.
On the other hand, the fact that he chooses to leave when his time is out shows you that he values his time. He values it more than the company, if you want to look at it like that.
Not everyone who works for you will love your company. For some people it's just a job. Now, it's your choice to make if that is good enough for you.
In any case, you make a good point. Basically he values a fraction of his time more than any negative, however big, inflicted on his company and his team members.