[tz] looking for information about changing time zone

[Paul Eggert]

On 9/7/20 2:50 PM, Françoise Kerjouan via tz wrote:
> I’m living in New Caledonia; our local government is thinking about changing
> time zone (from UTC +11 to UTC +12).

Yes, I saw that in the news a couple of weeks ago:

https://www.rnz.co.nz/international/pacific-news/424586/new-caledonia-plans-one-hour-time-zone-shift

That proposal would change the clocks on December 1. That is not a lot of 
notice, and most likely you'll run into some problems with cell phones and 
computers not getting updated in time.

> Could you please tell me how long a lead notice should be to be sure that
> the international community will get and process the information ?

Please see:

https://data.iana.org/time-zones/tz-link.html#changes

which says this:

If your government plans to change its time zone boundaries or daylight saving 
rules, inform tz at iana.org well in advance, as this will coordinate updates to 
many cell phones, computers, and other devices around the world. With less than 
a year's notice there is a good chance that some computer-based clocks will 
operate incorrectly after the change, due to delays in propagating updates to 
software and data. The shorter the notice, the more likely clock problems will 
arise; see "On the Timing of Time Zone 
Changes"<https://codeofmatt.com/on-the-timing-of-time-zone-changes/> for examples.