Time zones, daylight saving and the time on your certificate

October 31, 2026 · 5 min read

A sunrise is a single instant. Writing it down as a time of day needs one more decision: which clock. For a dedication, the answer is the local time at the place, the time a person standing there would read on a watch. Getting that right is less trivial than it sounds.

Time zones are political

Time zones follow borders and decisions, not longitude. China uses a single zone, UTC+8, across about 60° of longitude, so the sun rises after 09:00 in winter in its far west. Spain uses Central European Time although most of it lies west of Greenwich. India uses UTC+5:30 nationally; Nepal uses UTC+5:45. A few places have changed zone in living memory, and some have switched daylight saving time on or off several times.

So a sunrise’s clock time cannot be worked out from coordinates alone. It needs the rules in force at that place on that date.

Daylight saving time

Many countries move their clocks forward in spring and back in autumn, and not on the same dates. In 2026 the European Union changes back on 25 October; the United States and Canada on 1 November. In the Southern Hemisphere, places that use summer time change in the opposite seasons. A sunrise on 30 October in New York is still on daylight time; one on 2 November is on standard time, an hour earlier on the clock.

How Resthe finds the zone

Resthe looks up the time zone for the exact coordinates you pin, using boundary data from the standard tz database, the same data computers and phones rely on. There is no approximation by longitude: if the zone for a point cannot be found exactly, the order is not taken. The local time is then computed with the historical rules of that zone, including every past change to daylight saving time.

This matters most for Life Moments, which reach back in time:

• Your First Sunrise converts the local time of birth into universal time with the rules in force on the birth date.
• The Nth Sunrise counts every sunrise since the day you met, which may span several clock changes and occasionally a change of zone.

Edge cases the rules handle

• The missing hour. When clocks go forward, a local time such as 02:30 may not exist that night. A time of birth entered in that gap is not accepted as is.
• The repeated hour. When clocks go back, 01:30 can happen twice. The calculation has to know which.
• Places near zone borders. Two points a few hundred metres apart can be in different zones. The pin decides.

What the clock does to a sunrise

The same rules that set the clocks move the sunrise on the clock face far from what the sun alone would suggest. Calculated for real places:

• Kashgar, in China’s far west, runs on Beijing time. On 21 December 2026 the sun rises there at about 10:12 and sets at 19:35; on 21 June 2027 it rises at 07:29 and sets at 22:26. The sun is highest in the sky there at close to 15:00 on the clock.
• A Coruña, in Galicia, uses Central European Time although it lies west of Greenwich. Sunrise on 21 December 2026 is at about 09:02, and on 21 June 2027 the sun sets at about 22:17.
• Grand Canyon Village, Arizona, stays on standard time all year, so its summer sunrise, about 05:12 on 21 June 2027, reads the same on the clock as it would in Los Angeles on Pacific Daylight Time.

None of this changes the sunrise itself. It changes only the number written next to it, which is why the zone must be right.

The changes in 2027

For the year ahead, the main clock changes are:

Lord Howe Island, off the coast of Australia, changes its clocks by only half an hour. The Chatham Islands of New Zealand run 45 minutes off the hour, at UTC+12:45 in winter and UTC+13:45 in summer. Morocco keeps UTC+1 for most of the year but returns to UTC+0 during Ramadan; in 2027 that runs from 7 February to 14 March.

When the rules themselves change

Zones are changed by law, sometimes at short notice. The best-known example is Samoa, which moved from one side of the International Date Line to the other at the end of 2011; the country skipped Friday 30 December entirely, going straight from Thursday to Saturday. Other countries have abolished or reinstated summer time within the last twenty years. For a moment in the past, such as a birth or a meeting, the calculation uses the rules that applied then; for a moment ahead, it uses the rules as published today. If a government changes them after an order, the instant of the sunrise stays the same and only its clock time would read differently.

Why we store the instant

Internally every moment is stored as a single instant in universal time, the same everywhere on Earth, and the zone is applied only to display it. That keeps the moment itself fixed whatever happens to clocks. The local time on the certificate is a faithful translation of that instant, made with the rules for that place on that date.

On the certificate

The certificate shows the moment in local time at the place, with the date and the zone’s short name, such as GMT+2. The gift page shows the same local time with a countdown, which runs correctly wherever the recipient happens to be, so they always know how long is left.

You can pin any place and see the local time of the moment before you pay, with The Sunrise, or for a count since the day you met, The Nth Sunrise.