What science knows, and what it hasn’t settled.

1. What everyone agrees on

Changing the clocks twice a year has almost no defenders left: sleep specialists and the public alike want it to end, even if a few researchers still defend the logic of seasonal switching1. In the week after the March jump, fatal crashes rise by about 6% in the United States2, and a meta-analysis finds a slightly higher heart attack risk (relative risk of 1.04)3. A large U.S. study published in 2025, however, finds no significant rise in heart attacks4: these effects probably exist, but they are modest.

The key point: these risks come from the change itself. Keeping standard time or keeping daylight time eliminates them equally. So they are not an argument for either one.

2. The main argument for standard time: morning light

Favours standard time Solid mechanism

Our internal clock runs a little slower than 24 hours. Morning light resets it; evening light delays it. Controlled experiments show that the effect of light depends on when it is received5. This is the basis on which sleep specialists recommend standard time all year678, and on which a Canadian analysis published in October 2026 concludes that the health evidence leans toward standard time9.

This argument deserves to be taken seriously. But three things must be distinguished: the mechanism (solid), the light actually received by people who spend their winter mornings in a car, a bus or an office (little measured), and the health balance of a permanent time in Québec (measured in no known study). To get from the first to the third, research relies mainly on comparisons between neighbouring U.S. regions on either side of a time zone border: on the side where the sun sets later, people sleep about 19 minutes less10. It is a serious signal, but an indirect one: it comes from U.S. populations, with their own schedules, and does not directly predict the effect of a Québec choice.

A large systematic review published in 2026 (157 studies, 36 countries, search ending in June 2025) finds unfavourable, null and favourable effects, and rejects a uniformly negative portrayal of daylight time — without showing that it is better in winter. Its authors in fact lean toward standard time if clock changes are abolished11. Two sleep researchers have also called for honest communication of uncertainty and against alarmist messaging12.

3. What evening light brings

Fewer robberies Moderate evidence

In the United States, adding an hour of evening light goes with about 7% fewer robberies over the day, and 27% fewer in the hour that gains the light13. In Chile, the drop reaches about 30% between 7 and 9 PM14; in Montevideo, it is larger in poorly lit neighbourhoods15. These results concern certain crimes at certain hours: no claim is made that daylight time reduces all crime.

More visible pedestrians at rush hour Moderate evidence, mixed results

Pedestrians and cyclists are the road users most sensitive to darkness16. U.S. models estimate that year-round daylight time would reduce pedestrian deaths in the affected hours (about 13% according to one study)1718, and a British study puts the drop in the costs of darkness-related crashes at about 8%19. In Québec, 75 pedestrians were killed in 2025, and the SAAQ points to the role of fading light in the fall20. Caution: a systematic review judges the studies too heterogeneous to put a number on the net balance21, and darker mornings have a cost too. According to the SAAQ, between 5 and 8 PM, crashes injuring a pedestrian rise by 97.7% in the 30 days after the clocks fall back, compared with the 30 days before22. This comparison does not isolate the effect of the clock, since the season changes too, but it shows how much rush-hour darkness exposes pedestrians.

Slightly more active children Moderate evidence, small effect

Among 23,000 children in nine countries wearing accelerometers, lighter evenings go with a little more physical activity23. The average effect is small and varies from country to country. It concerns a generation whose aerobic fitness has dropped since 1982 by about 18% in boys and 12% in girls aged 1724. In adults, studies find no rise in the total: people shift their activity toward the evening instead2526.

More light while we’re awake Original calculation, Statistics Canada data

Using the sleep hours reported by Quebecers aged 15 and over in the Time Use Survey, and if everyone keeps them, daylight time gives Montréal 233 more hours of light a year while awake than standard time: about 127 hours less in the morning, 360 more in the afternoon and evening2728. This is available light, not a biological dose: an hour of light in the morning does not act on the internal clock the way an hour in the evening does. The calculation and its limits

November blues Signal to be confirmed

In Denmark, hospital-treated depression episodes rise by about 11% after the clocks fall back in the fall, for about ten weeks29. A 2025 English study instead finds drops in some health events after that change30. The signal exists, but it remains to be confirmed.

A value that medical records don’t measure

A walk in daylight after work, a game of hockey on the neighbourhood rink, a drink on the patio: these moments have value in themselves, even if they appear in no medical record. That is perhaps the strongest argument for daylight time, precisely because it promises nothing fragile.

4. Winter mornings: the response

With daylight time, the sun would rise around 8:30 AM in southern Québec at the solstice. Teenagers are the most affected: they already lack sleep after the March jump31, and their school results are better when school starts later relative to sunrise32.

If daylight time is chosen, it must come with:

• later start times in high school, a measure recommended for teens whatever the time zone: the American Academy of Pediatrics recommends not starting before 8:30 AM33, California made it law34, and Christian Duval (UQAM) proposes starting one hour later from December 1 to March 135;
• better-lit, safer routes to school in the morning;
• bright light in the morning in workplaces, as researchers recommend for adults36, and an assessment of its value in schools;
• independent monitoring (sleep, road safety, health) with a review clause.

These are the measures the 2026 Canadian analysis proposes to provinces that choose daylight time9. They aim to reduce morning risks; their effect will need to be measured. One detail matters: if school starts and ends one hour later, the students concerned do not also gain an hour of play in daylight after class. The evening gain remains whole for everyone else: younger children, parents, workers.

5. Spectacular figures to set aside (on both sides)

• “Daylight time reduces mortality in Europe.” The study that suggested it was retracted on May 28, 20263738. It supported daylight time: this site does not use it.
• “Standard time would prevent millions of obesity cases and hundreds of thousands of strokes.” These figures come from a computer model, not observed cases. They compare each permanent time with the current clock changes: between permanent standard time and permanent daylight time, the projected gap for obesity was already only about 0.9 million people in the United States, in prevalence and not per year3940. The model was then corrected (it let the sun shine… at night)41. According to a critique published in October 2026, a second corrected error brings the gap in its indicator between the two times down to about 0.2 hours per person per year42. The model’s authors defend their approach, while acknowledging that it does not establish cause and effect434445.
• “Living in the west of a time zone gives you cancer.” A reanalysis with new data does not find most of these associations again4647. And the International Agency for Research on Cancer’s classification concerns night work, not daylight time48.
• “Daylight time increases heart attacks by 24% and strokes by 8%.” The first figure concerns the Monday after the March jump, in Michigan49; the second, the two days after a clock change, in Finland50. These are transition effects: both permanent times remove them. They say nothing about which time to keep.
• “Sleep specialists have no evidence.” Also false: the role of morning light is well established, and their recommendation is serious56. What is missing is a measure of the full balance of the two permanent times.
• “Daylight time saves electricity.” Not demonstrated for Québec5152. This site does not claim it.