Daylight Saving Time and International Law

When I teach the introductory international law class to my students, one of the more difficult aspects of the discussion is the line between customary state practices that rise to the level of binding norms, and those that do not. We all teach Paquete Habana, and the students’ eyes glaze over as we passionately discuss the law of prize and the vexing problem of whether coastal fishing vessels must be left alone to ply their trade. When the students ask for modern examples of state custom that is not obligatory, we struggle for examples and cite to emerging human rights norms that are not yet obligatory, but should be. But even those examples do not illuminate a custom that most of us would say should remain non-binding. Where are the examples of state practices that are widely respected, but not out of a sense of legal obligation? There is one obvious example. It is daylight saving time (DST).

Humor me if you will and look at DST from the perspective of customary international law.

Emergence of the Custom. When did the custom of DST first emerge? We know the precise moment: April 30, 1916, at 11:00 p.m. (GMT). Actually, in 1784 while living in Paris, Ben Franklin proposed the idea of shifting work hours in the summer months to maximize the use of daylight (the Parisians slept until noon), but his idea was not to change the clocks, but rather to ration candles and levy a tax on the use of shudders. In 1907, a Londoner by the name of William Willett vigorously campaigned for the adoption of DST, lamenting that everyone regrets that the “bright light of an early morning during Spring and Summer months is so seldom seen or used.” Germany adopted the practice of DST as a wartime measure to conserve energy in April of 1916, and over a dozen countries quickly followed suit.

General and Consistent Practice. Ninety years later over 70 countries have adopted the practice of DST. There is a clear consensus among states to accept this custom, as exhibited by widespread conduct among the nations of the world. Almost every industrialized nation of the world now employs the practice, affecting over one billion people. Its goal, to use daylight to its maximum advantage, is generally recognized to be of universal benefit.

No Opinio Juris. But there is quite clearly no suggestion that states adhere to this practice out of a sense of legal obligation. For example, China never adhered to DST until 1986, tried it for a few years, and then abandoned the idea in 1991. There is no suggestion that China was a consistent objector prior to 1986, or that it violated customary international law when it dropped the practice in 1991.

Regional Custom. Finally, there is one other aspect of DST that is interesting: it is clearly divided into three regional customs. Go to this link and scroll across the globe you will see why. The Northern Hemisphere adopts the practice of DST in their spring and summer (April to October), the Southern Hemisphere adopts the practice in their spring and summer (October to March), and the equitorial tropics, having no need for it, do not adopt the practice at all.

To invert the language of Paquete Habana, this review of the precedents and authorities on the subject appears to abundantly demonstrate that at the present day, by the general consent of the civilized nations of the world, daylight saving time is not an established rule of international law. But perhaps “the period of [another] hundred years … [will prove] amply sufficient to … enable[] what originally … rested in custom or comity, courtesy or concession, to grow, by the general assent of civilized nations, into a settled rule of international law.”