World Clock

How to Use the World Clock

1. Scan the default set of cities - the board starts populated with six common zones so you see a working clock immediately.
2. Add a zone via the "Add timezone" dropdown; pick any IANA identifier and hit the add button to append a new row to the board.
3. Remove a zone with the small close control on each card when you no longer need it on screen.
4. Watch it tick. Every card updates once per second, driven by a setInterval loop reading new Date(). Each card also shows the current UTC offset so you know at a glance how far apart two regions are.

What Makes This A Dashboard, Not A Converter

The world clock is built around the present instant: every card asks "what time is it right now in this zone?" and repaints on the clock tick. There is no source date, no target date, no conversion math in the user's hands. Internally each card is a useEffect-driven interval that re-renders using Intl.DateTimeFormat with a fixed timeZone option. Because Date.now() is a single monotonic-ish epoch value and each card derives its display from that same source, every card stays perfectly in sync - you cannot have Tokyo one second ahead of Sydney by accident. The offset label comes from the same Intl API with timeZoneName: 'shortOffset', so DST transitions flip the label live without a page reload.

Why People Keep A World Clock Open

• Running a distributed on-call rotation where you need to see at a glance whether the next responder is awake.
• Trading across global market hours - NYSE, LSE, TSE, HKEX overlap and gap at specific moments and an eyeball check is faster than math.
• Coordinating a multi-office release when you want to wait until APAC is online before flipping a feature flag.
• Running a family clock on a tablet in the hallway so kids can tell whether it is acceptable to call grandparents abroad.
• Giving customer support reps visibility into when a region-specific incident started, relative to a local business hour.
• Planning when to drop an X, LinkedIn, or TikTok post for maximum reach in a specific timezone.

Things That Surprise People Running A World Clock

• Cards in "the same country" can disagree. The USA spans six standard timezones (including Alaska and Hawaii); Russia spans eleven; Canada spans six. Picking "United States" is not a choice; picking America/New_York vs. America/Chicago is.
• DST flips happen at different local times. Europe springs forward at 01:00 UTC, while North America does it at 02:00 local - so for one week in March, the usual 5-hour gap between London and New York is 4 hours, then snaps back. Your board will reflect that without you touching anything.
• Your system clock is authoritative here. If the device drifts (old laptop with dying CMOS battery, ESP32 without NTP), every card on the board is wrong. We do not fetch a reference time from a server.
• The Arctic and Antarctic have weird rules. Several Antarctic research stations adopt the timezone of their resupply country, and can change when the flag on the base changes.
• Counting days across zones is harder than counting hours. At 3:00 AM London on December 15, it is already December 15 in Auckland but still December 14 in Los Angeles. A naive "today's date" label on a world-clock card has to be per-zone, not shared.

Civil Time, UTC, and Why This Board Is All Different

The board shows civil time in each zone, not UTC. UTC (Coordinated Universal Time) is the global reference, defined by atomic clocks with periodic leap seconds; GMT is the historical predecessor still used in some UK contexts. Civil time is UTC plus a political offset that includes DST. The IANA tz database (the Olson database) is the authoritative catalogue - when Samoa skipped December 30, 2011 to jump the International Date Line, or when Turkey dropped DST in 2016, the database recorded it and your browser shipped the update. Identifiers follow the Continent/City format because EST and CST are ambiguous across regions.

World Clock Widgets Compared

macOS Calendar and Windows 11 Clock both offer multi-timezone widgets built into the OS; they are great if you live in one ecosystem but do not travel well to a shared screen or a guest laptop. Worldtimebuddy.com and Every Time Zone offer sliders for planning meetings - better than a pure live board when you need to scroll through a working window and see overlap. Command-line watch -n 1 "TZ=Asia/Tokyo date" works for a tmux obsessive but does not scale past two zones. This page is the right pick for a browser-tab or a wall-display board: it runs anywhere a browser runs, it updates without refreshing, and adding a zone is one dropdown click. If you need a specific moment translated across zones (not "right now"), use the Timezone Converter - that is the other half of the pair.