Same clock, different calendar

A zero-hour time difference feels like the scheduling problem is over. It is over for the clock. It is not over for the calendar. The pairs below show the same time, or one stable hour, and they still produce empty rooms. The cause is a holiday, a storm warning, or a festival dated to the moon.

The overlap grid on a pair page will light up green for most of the day. Believe the grid about the hours. Do not believe it about whether the office is staffed. The grid does not know Canada’s Thanksgiving from the US one, and it does not know that a typhoon signal is up.

New York and Toronto

New York and Toronto are the same time all year. Both change on the second Sunday of March and the first Sunday of November, so the gap does not even open for a mismatch week. A 9:00 AM call is 9:00 AM. The exchanges trade in the same hour.

The holidays are in different weeks, on purpose. Canada’s Thanksgiving is the second Monday of October. The US Thanksgiving is the fourth Thursday of November. A Monday off in Toronto is a normal Monday in New York, and a Thursday off in New York in late November is a normal Thursday in Toronto. Canada Day empties Canadian offices and does not appear on a US calendar. Boxing Day is a statutory holiday in Canada. Provincial holidays, including Ontario’s long weekend in February, are invisible if you only subscribed to a US holiday feed.

Before you send a cross-border workshop invite, open both public-holiday lists for that month. The flight is about ninety minutes. The list takes longer to check, and it is the check that matters. The clocks will agree with each other the whole time you are wrong about the date.

Seoul and Tokyo

Seoul and Tokyo are both UTC+9, with no daylight saving on either side. The flight is about two and a half hours. People treat it as domestic, which is fair for the clock and careless for the calendar.

Korea closes for several days around Chuseok, the harvest festival on the 15th day of the eighth lunar month, and again around Seollal, the lunar new year. In 2025 the main day of Chuseok was October 6, which is not a date you can reuse. The lunar date moves by weeks on a Gregorian calendar. Those weeks are working weeks in Tokyo. Japan’s break around mid-August is not a Korean holiday. Japan’s cluster of public holidays in late April and early May is only partly shared, if it is shared at all. A joint sprint planned for “sometime in September” or “the week Japan is off in August” needs both calendars on the table. Last year’s plan is not this year’s plan.

Hong Kong and Tokyo and Beijing and Tokyo are the one-hour versions of the same mistake. The hour is stable and small. The holiday lists are not the same list.

Hong Kong and Singapore

Hong Kong and Singapore share UTC+8 and never change it. A 10:00 AM call is 10:00 AM. Regional headquarters run the pair like one city with a four-hour flight in the middle.

Weather breaks it. When the Hong Kong Observatory hoists typhoon signal No. 8, or the black rainstorm warning, most offices close. Singapore does not have an equivalent signal, and a clear afternoon there is not evidence that Central is open. The Hong Kong stock exchange follows its own typhoon notice, which can disagree with a specific office’s decision to send people home. If the week has a hard deadline, write down what happens when signal 8 goes up. Discovering the policy in the chat, during the signal, is how the deadline moves.

Public holidays diverge in quieter ways. Singapore’s National Day is in August. Hong Kong’s Christmas shutdown is not Singapore’s. Neither side inherits the other’s red days just because the clocks match.

Beijing and Singapore

Beijing and Singapore are the same clock, and the same warning applies to anyone who tries to “correct” a colleague in western China onto a different offset. China uses one civil time zone. Singapore is not a half hour off Beijing. If the times on a laptop disagree, one laptop has the wrong zone.

Lunar new year is the break that surprises Singapore. Mainland offices close for about a week, and the State Council’s notice also names makeup workdays, so a Saturday on the edge of the holiday can be a workday. Singapore’s public holiday for the same festival is two days. A deadline set inside the mainland week will not get a Beijing reply. A Beijing plan that assumes Singapore has also vanished for the week is wrong in the other direction. The lunar date moves. Read the notice for the year you are planning, not the week the festival “usually” falls in.

What to add to the invite

For any of these pairs, the time field is the easy part. Add one line under it: which holiday lists you checked, and the date you checked them. A workshop on a Monday should say “Toronto in, New York in” or it should not be on that Monday. A week that might be Chuseok should name the year. A Hong Kong deadline should say what signal 8 does to it.

The hours themselves, including pairs that are one hour apart rather than zero, are on the city pages linked above. How to read the green rows when the hours do not match, which is the opposite problem, is in reading a business hours overlap matrix. India’s half hour is a third problem, and it is not solved by noticing that two Asian capitals agree: scheduling with India.

If the team is large enough that “check the holidays” has become a slogan, put the year’s days off into the working agreement next to the overlap hours. The remote team scheduling guide is where that agreement sits. A zero-hour pair still belongs in it. The clock being easy is how the holiday gets skipped.