When you choose to be the CEO of a company and you hire employees, you're no longer just working for yourself. How a CEO spends his time means everything to the company and its employees.
I don't know how you would you feel if you worked at the OP's startup, but I would have a problem with the notion that the person ultimately responsible for making payroll found it worthwhile and enjoyable to spend 45-plus minutes defending his views on startups and arguing with a person who wanted him to sign an NDA about an unrelated business idea.
It's not the 45-plus minutes, it's how he chose to spend them.
This is a very narrow view of mentorship. Mentorship is incredibly selfish: often the person doing the mentoring gets more out of the conversation than the mentee...case in point. Here, the author was challenged on basic ideas that led him to think more broadly about what he assumed was obvious. This could and often does lead to more creative thinking and applications in his company. As long as he doesn't do this all the time, I think it's silly to assume that a CEO should spend 24/7 working on a company. In fact, it's degenerative, unhealthy, and produces poor results for companies (as many studies show).
Personally, I think there should be more focus on when he did it rather than the fact he did it. If he was at the office doing this, then I'd agree with you. If the workday was done, then I can see an hour of his personal time being fine.
I don't know how you would you feel if you worked at the OP's startup, but I would have a problem with the notion that the person ultimately responsible for making payroll found it worthwhile and enjoyable to spend 45-plus minutes defending his views on startups and arguing with a person who wanted him to sign an NDA about an unrelated business idea.
It's not the 45-plus minutes, it's how he chose to spend them.