An ever-increasing proportion of the French working population today has working hours that are no longer subject to the explicit diktat of their employer. However, in Île-de-France (Paris region), the problems of morning rush-hour congestion continue to worsen. Before trying to solve peak congestion problems, therefore, we need to understand the underlying reasons behind an individual work schedule choices. Why does a person on flexitime commute during rush hour? Our research adopts an interpretive approach and focuses on daily scheduling demands. It draws on the results of a survey (3202 respondents) and interviews (29) with management level employees working in the Plaine Saint-Denis business district. In describing the temporal strategies that explain voluntary peak-hour commuting, we find results along three dimensions: (I) there are coupling constraints (school times, meeting times) that force workers with flexible hours to commute during peak hours; (II) workers with flexible hours and fewer coupling constraints prefer to arrive before or during rush hour in order to enjoy late afternoon activities with family and friends; (III) there are social norms on working hours (ideal of the disciplined worker or the dedicated executive) that limit flexibility by frowning on those who arrive overly late at the office. In conclusion, by revealing the organic intricacy of the factors that lead to synchronisation, our article is able to generate operational recommendations for reducing congestion at peak hours.