If anything, Musk has two full time jobs (priorities: 1. SpaceX; 2. Tesla; 3. everything else) and actually does 80-100 hours per week of work. He's not out creating vanity designer clothing lines in his spare time.
You can't create world class products or companies while maintaing a silly "because i'm so special i'll only work 6 hours a day, 4 days a week, 1 week a month" mindset.