Timezone Converter World Clock

Timezone converts a moment between places, keeps a world clock of the cities
you care about, and finds the hours when everybody is awake at once. It works
with no connection at all.

WHAT MOST TIME ZONE APPS GET WRONG

A time zone is not a city, and an offset is not a time zone. A zone is a rule:
a history of offsets and the dates they changed. Almost every converter here
ignores that, looks up two offsets, subtracts them and adds the difference to
the time you typed. That is wrong three ways:

• It uses TODAY'S offsets for a date in July. London is UTC+0 now and UTC+1
then.

• It uses one country's changeover dates for another. America moves its clocks
three weeks before Europe does, so for three weeks every March New York is
four hours behind London, not five.

• It cannot represent the answer at all when the local time it was handed does
not exist, or exists twice.

Here, converting is reading one point on the timeline in another set of rules.
There is no arithmetic to get wrong.

THE TWO MORNINGS A YEAR

On the morning the clocks go forward, an hour of local time does not happen.
There is no 2:30am in New York on 8 March. On the night they go back, an hour
happens twice: 1:30am in London on 25 October is two different moments, sixty
minutes apart.

Almost every app handles this silently — it shows 3:30 when you typed 2:30, or
picks one of the two 1:30s and never mentions the other. This one says so, in a
sentence, and lets you take the second.

It also knows Britain loses a different hour from America: the clocks go
forward at 1am there, so 2:30 is an ordinary time in London that morning and a
missing one in New York.

WHEN CAN WE ALL TALK

Pick two to five places and say what hours each of them works — nine to five,
eight to four, or ten at night to six in the morning. The app shows every
stretch of the day that is inside everybody's window.

It handles the day boundary, because it never works in local dates: Tokyo's
Monday morning really is Los Angeles's Sunday afternoon. And when there is NO
overlap — the honest answer for the Pacific against the American west coast on
office hours — it says so in words, rather than showing an empty strip you will
assume failed to load.

Places forty-five minutes off the hour work properly: India, Nepal, the Chatham
Islands and Eucla are real, and a three-quarter-usable hour is shown as one.

THE CLOCKS

Every city you add, ticking: the local time, whether it is yesterday, today or
tomorrow there, and how far ahead or behind you it is. Every row recomputes
itself every second, so land somewhere and the whole list re-reads itself
against your new zone.

SEARCHING

Type a city, not an abbreviation. Accents do not matter: sao paulo finds São
Paulo and zurich finds Zürich. Abbreviations are never an input, because they
cannot mean one zone — CST is three zones and IST is two — though the app will
show you one beside a place you chose.

The whole IANA database is in the app: every zone, every historical offset.
Nothing is fetched.

ALSO

• 12-hour or 24-hour, or follow the phone
• Compare against the phone's zone, or pin one while you are away
• Light and dark, and Material You if you want it
• Save a copy of your list to a file — this is how you move to a new phone

WHAT IT WILL NOT DO

No location, ever. Detecting which zone you are standing in is the flagship
feature of the paid rivals here and it is refused: the phone already knows its
own zone for free, and every other place on your list is one you typed.

No account, no sync, no server, and no notifications — nothing here will ever
interrupt you. Uninstalling deletes your list, and Save a copy is how you move
it.

Three permissions, all of them for the ads that keep it free.