Mark Zuckerberg Reveals the Surprising Length of His Workday at Facebook

— -- Mark Zuckerberg may be a billionaire CEO, but the amount of time he spends in the office is surprisingly close to normal.

In an unannounced question-and-answer session Tuesday night on his Facebook page, Zuckerberg, 30, said he spends about 50 to 60 hours per week in the office and at meetings.

But then again, to Mark Zuckerberg, what is work?

"If you count all the time I'm focused on our mission, that's basically my whole life," he said.

"I spend most of my time thinking about how to connect the world and serve our community better, but a lot of that time isn't in our office or meeting with people or doing what you'd call real work," Zuckerberg said. "I take a lot of time just to read and think about things by myself."

Zuckerberg gave another glimpse into life as a CEO last month during a town hall when he revealed the one question he asks before making any key Facebook hire.

"I will only hire someone to work directly for me if I would work for that person," Zuckerberg told a group in Barcelona that participated in the Facebook co-founder's monthly town hall meeting. "It's a pretty good test."