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Libya changed time with days of notice
An Hour Out
The notice was too short for anyone to get an update out in time. It did not matter which operating system a computer ran: every one in the country showed the wrong hour.
Reading The News
Governments change time zones more often than most people would guess, apparently many times a year, and sometimes several times in a single year as governments change over. A programmer who handles time zones ends up subscribing to the list of upcoming changes and reading the news for the next one.
Short-Notice Rules
When the Libya story broke, that meant reading the article and hurriedly coding the change in. A calendar of known rules does not help when the rule itself arrives two days before the clocks.
How do computers get new time zone rules?
A public mailing list collects government announcements, and volunteers fold them into the IANA time zone database. Operating system and phone makers then ship the updated data inside their regular updates. Devices that rarely update, such as embedded equipment, can keep the old rule for months. That delay is why a short-notice change leaves some machines showing the wrong hour.
Which governments have changed time most abruptly?
Russia moved to permanent summer time in 2011 and then shifted back an hour to permanent standard time in 2014. In both cases the change reached computer systems with little warning compared with the long lead times of older rules. Venezuela shifted its clocks by half an hour in 2007 and reversed the change in 2016. Each of these changes became a new entry in the shared database.
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