When it comes to balancing his five ventures — SpaceX, Tesla, OpenAI, Neuralink and the Boring Company — Musk says at one point he used to work up to 100 hours a week (for reference, there are 168 hours in a week). Nowadays, Musk commits to working a mere 80 to 90 hours a week. During Tesla’s annual shareholder meeting earlier this month, Musk said he spends 90 percent of his time divided between SpaceX and Tesla and the remaining less than 10 percent on everything else.

During a 2013 interview at South by Southwest, Musk said he responds to emails while also interacting with his children because they were at an age where they didn’t require his undivided attention, reports Business Insider.

As part of a speaker series at the Computer History Museum in 2013, Musk noted having a smartphone has been helpful because whether out at drinks, in other social settings, in a car, while walking or in the bathroom, you can do email anytime while you are awake.

During his 100-hour work weeks, Musk says he would drink eight cans of Diet Coke and fuel up on several cups of coffee. He says he has since cut back and despite working twice as many hours as most Americans, he manages to get about six or six and half hours of sleep.

“Sleep is really great, I find if I don’t get enough sleep then I’m quite grumpy,” Musk said during his Computer History Museum talk. “I found that I can drop below a certain threshold of sleep and although I would be awake for more hours and I could sustain it, I would get less done because my mental acuity would be affected.”

In comparison to other executives, Musk doesn’t make sleeping a priority. Jeff Bezos says he getting eight hours of sleep makes a big difference for him. “If you shortchange your sleep, you might get a couple of extra ‘productive’ hours, but that productivity might be an illusion,” Bezos says.

Perhaps Musk can take a pointer from his senior self-made billionaire Mark Cuban, who went through phases of “all work, all the time” like Musk.

“I think entrepreneurs go through a process. When I was all in and I was starting companies, I would dream about work. And literally, I’d wake up and I’d have to do things … it just consumes you,” says Cuban. “And I think entrepreneurs go through that process; creative people go through that process.

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