We develop a new survey instrument to codify CEOs' diaries in large samples and use it to measure the labor supply of 1,114 family and professional CEOs of manufacturing firms across six countries (Brazil, France, Germany, India, the United Kingdom and the United States). By this measure, family CEOs work 9% fewer hours relative to professional CEOs, even when we control for a wide range of CEO, firm and industry characteristics. The differences in hours worked between family and professional CEOs are larger when the opportunity cost of leisure is lower. We interpret these results as evidence of differences in preferences for leisure across CEOs rather than optimal responses to organizational differences correlated with ownership. Differences in labor supply are larger in countries where inheritance laws favor wealth concentration and are correlated with differences in firm performance.