At this moment, the U.S. and U.K. are an hour closer than they typically would be. For this temporary contraction of temporal borders, you can thank the differing application of Daylight Savings Time. The United States began DST at 2am on Sunday, March 12th. The UK won’t begin DST until 1am this Sunday. So right now, for these two weeks in March, the US and the UK are, in the sense of time if not in space, closer to each other.

For those without business across the pond, this change has no meaningful effect. But for the British who work across waves, meetings with American counterparts are blessedly an hour earlier. A meeting set at 4pm ET now occurs at a more respectable post-prandial 8pm GMT, instead of an awfully-close-to-bedtime 9pm GMT.

This allows commerce to move a bit more fluidly.

The two countries may remain in their same geographic locations, but temporally speaking, the border between the two nations has drawn closer—as if the eastern seaboard had stretched ever so slightly out into the Atlantic, and the island of England, taken up anchor, had drifted ever so slightly west.

Every time zone, as you’ll recall, is defined as an offset from Coordinated Universal Time (UTC). Coordinated Universal Time begins at 0 degrees longitude, that imaginary line that passes through the Royal Observatory in London. The earth rotates 15 degrees per hour and each of those 15 degrees is a time zone, ranging from UTC−12:00 (Baker Island, in the middle of the Pacific) to UTC+14:00 (also in the middle of the Pacific).

The offsets are usually a whole number of hours, but a few zones are offset by an additional 30 or 45 minutes. This is because time zones tend to conform to boundaries between and within nations instead of strictly following longitude. Getting things done locally trumps regulations globally every time.

The state of Indiana, famously, observes Eastern time except for 12 of its 92 counties. Folks in the northwest live near Chicago. Chicago is on Central Time. Central Time is more convenient for all involved. Folks in the southwest live near Illinois and Kentucky. Illinois and Kentucky are on Central Time. Central Time is, again, more convenient.

China, also famously, maintains one official time zone across its 3100 miles from east to west. One time zone, to Mao Zedong, symbolized national unity. One time zone was more convenient.

Some countries splice their time zones into thirty-minute increments. All of India lies in the time zone UTC+05:30, and accordingly, every fifth person in the world lives in a time zone with a fractional offset. Neighboring Nepal is at UTC+05:45, so if you were to cross the border from India time would jump 15 minutes forward. If you were to travel one hundred miles further north and continue into China, time would jump 2 hours and 15 minutes forward. None of these countries practice DST and so, at least temporally speaking, their borders never change.

A general rule of thumb, however, is that bordering countries trying to increase trade will sync their clocks. Consider, for example, Mexico. Mexico has four time zones. Those time zones roughly correspond to the time zones of the United States. The catch is that Mexico recently stopped observing DST.

Up until March 12th of this year I, a resident of Mexico City in Zona Centro (UTC-0600), was only one hour behind New York on Eastern Standard Time (UTC-0500). But since March 12th, Mexico City is now two hours behind New York (UTC-0400). We will continue to be two hours behind until DST ends Sunday, Nov 5th. This will make my zoom schedule with New York clients just a bit more onerous, making my residency in CDMX the temporal equivalent of, oh let’s say, Salt Lake City.

Tempus fugit, but also expandeth, and now I can’t get out of bed as late as I used to.

Mexico can’t separate itself entirely from the U.S., however, so there are parts of this country that continue to practice Daylight Savings Time. Those parts include Baja California and municipalities within 20 km of the border, meaning places like Tijuana, Mexicali, and Chihuahua.

In those cities, they match the time zone of their northern neighbors, a kind of temporal air lock that equalizes the cross-border pressure. I could change my time +1 UTC right now just by driving a few degrees latitude north to, say, Ciudad Juárez. The border I would find there certainly isn’t demilitarized, but you could say it is, at least for the moment, a zone that has been de-temporalized.