Thank you very much ! -----Message d'origine----- De : Brian Inglis [mailto:Brian.Inglis@SystematicSw.ab.ca] Envoyé : mercredi 9 septembre 2020 04:23 À : tz@iana.org Cc : Françoise Kerjouan Objet : Re: [tz] looking for information about changing time zone On 2020-09-07 15:50, Françoise Kerjouan via tz wrote:

Madam, Sir,

I’m living in New Caledonia; our local government is thinking about changing time zone (from UTC +11 to UTC +12).

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 ?

I understood that the ICAN TZ database is widely used, but I didn’t catch if it is also used for international transports (by airports for example). Could you please tell me if it is the case? If not, whom should I ask for?

https://en.wikipedia.org/wiki/List_of_airports_in_New_Caledonia Your airports serving regular scheduled flights, the airlines servicing them, and your air service regulators, are responsible for informing IATA of various changes affecting local times of schedules, with the contracted notice for IATA to update their master schedules, and update subscribers by issuing updated IATA SSIM Standard Schedules Information Manual: https://www.iata.org/en/publications/store/standard-schedules-information/ As NC is a TOM of France governed by the DGOM, they may have control over time changes and those responsibilities may be theirs. For all other purposes, from clocks and mobile phones to almost all larger computer systems, providing all the same details here with a few months notice, will allow time for the global time zone data base maintainers here, and downstream major and minor systems and product providers, to make, test, and deploy changes, that will allow personal and small to enterprise systems, databases, and other products (like mobile, desktop, and enterprise calendar and scheduling programs) to properly handle the time change when it occurs. This will facilitate people making it onto their (possibly rescheduled) flights. If governments could let this mailing list know as soon as possible of any changes, there would be many fewer disruptions to their citizens lives and schedules, and those who communicate with them. -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada This email may be disturbing to some readers as it contains too much technical detail. Reader discretion is advised. [Data in IEC units and prefixes, physical quantities in SI.]

* Paul Eggert:

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@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.

Note that the notice period of one year is from the time the rule change becomes official to when the difference becomes observable in practice (in other words, when the rule change becomes effective). This is not the same as the time from the start of the entire process to the time it becomes effective, but this is the way most officials appear to interpret it. Most rule change proposals are in legal limbo for a long period of time, and close to all of them fail to become effective. This means that distributors of the time zone database can do little to prepare when the process starts. Instead, they have to wait until changes become official. Only at that point, it is possible to distribute updates that change time zone rules for future dates. One thing that might also come as a surprise (particulaly for DST changes or any change at a DST boundary) is that the database format is sufficiently flexible to express a rule change at an arbitrary future date. It is not restricted to making the change at the next DST transition. This means that distributors of the time zone database can act on any official change immediately, making full use of the notification period. Thanks, Florian -- Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn, Commercial register: Amtsgericht Muenchen, HRB 153243, Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill

On 9/10/20 3:49 AM, Robert Elz wrote:

Don't decide to fiddle with the time unless you're absolutely committed to doing that.

Yes, and thank you and Florian for pointing out gaps in the current text. I installed the attached to try to close the gaps.