The seasonal time change synchronises the start of human activity with morning light (dawn), allowing more daytime leisure in summer afternoons. This is the focus of the article that Jorge Mira Pérez and José María Martín Olalla, professors at the University of Santiago de Compostela (USC) and the University of Seville (US), have just published in the Journal of Sleep Research. In the article, they analyse the naturalness and usefulness of the seasonal time change in response to a position statement manifesto issued by the British Sleep Society (BSS) that calls for the end of the time change in the United Kingdom and the permanent adoption of winter time.

The researchers review the history of seasonal time change in the UK, highlighting its almost uninterrupted application since 1916, making it an optimal case for describing the application of time change and its effects. They point out that for more than a century the time change has provided a natural experiment in adapting the working day to the seasons, allowing an extra hour of daytime leisure in the summer evenings.

"If the population had perceived a chronic misalignment during daylight saving time, they would have counteracted it by changing their habits".

Based on time-use surveys, the authors point out that the collective acceptance of the time change is demonstrated by the fact that, in 100 years, British society has neither eliminated nor counteracted the change by seasonally adjusting its timetables. Referring to a typical working day in the UK, the study recalls that "since 1916 the British have preferred a seasonal adjustment with 9 to 5 in winter and 8 to 4 in summer, which thanks to the time change remains 9 to 5; with the advantage of a constant social reference throughout the year (9 to 5) and, at the same time, a seasonal adaptation". The authors add that the predictions of the original proponents of the practice seem to have been fulfilled: people appreciate starting their working day closer to dawn and thus being able to enjoy more daytime leisure time during the summer evenings. "If the British population had perceived a chronic misalignment during the summer time months, they would have counteracted it by changing their habits".

Martín-Olalla and Mira point out that the BSS subscribes to the rationale for the time change in its position statement manifesto: morning light plays a crucial role in our daily activation. The BSS emphasises this role in winter to rule out permanent daylight saving time because of the morning darkness it would cause in winter. The nuance that the BSS and other similar societies forget is that the sun rises earlier in summer, which encourages an earlier start to human activity: in the UK, in the summer, the sun rises at least four hours earlier than in winter. Martin-Olalla and Mira point out that the function of the seasonal time change is to adapt work activity to the morning light of each season.

The authors conclude by pointing out that in the current discussion on the seasonal time change the polls show a majority in favour of summer time over winter time. "This is another indication that the 1916 seasonal proposal continues to be accepted, now by today's generations. It's like an outcry: we love our current summer time schedules, please don't move it them back."