[tz] America/Mexico_City incorrect DST end time for 2018.

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Fri Dec 28 17:16:09 UTC 2018

On 2018-12-28 00:02, demxic wrote:
> El mar., 25 de dic. de 2018 a la(s) 13:06, Paul Eggert escribió:
>> demxic wrote:
>>> I would like to draw your attention to the fact that Mexico's City
>>> Daylight time ended on October 28 2018 03:00 AM local time. That is the
>>> exact moment when clocks moved backward to 02:00 AM.
>> What's your source for this information? CENAM 
>> <https://www.cenam.mx/hora_oficial/> says "el horario de verano inicia el 
>> primer domingo de abril a las 2h00 de la mañana, momento en el cual los
>> relojes se adelantan una hora, y termina el último domingo de octubre a las
>> 2h00 de la mañana, instante en el que los relojes se atrasan una hora." This 
>> suggests that daylight saving time ends at 02:00, not 03:00.
> Thank you for your quick response.
> It seems like CENAM information has not been updated for a while, I cannot find
> any official source but it was in newspapers all around and I am living in
> Mexico City and witnessed the change.

How did you witness the change? Did you see clocks being manually reset?
When people change clocks may be unrelated to the official timekeeping rules
which apply to legal situations, and may differ depending on regulations e.g.
the BIVA/BMV stock markets keep US time.

Timekeeping in Mexico varies as it follows US zones, dates, and rules near the
US border and Mexican zones, dates, and rules farther away; as articles will
vary with who writes, where they are based, whether they know enough to write
comprehensively or customized for target locations, or may lack knowledge and
skip research.
The lack of specificity in these articles argues for the latter - a hundred or
few words about the time change.

If CENAM information has not been updated for a while, perhaps there have been
no significant legal changes announced by federal or state governments.
The tzdb maintainers are reluctant to base any changes on often vague statements
 in online articles, requiring at least semi-official press releases with
comprehensive details, preferring links to or publications of officially enacted
laws or regulations in official gazettes or registers by the responsible
timekeeping or standards agency or ministry.

> https://www.marca.com/claro-mx/trending/2018/10/22/5bccfb0a46163fe0528b460d.html
> Un nuevo cambio de horario 
> <https://www.marca.com/claro-mx/trending/2018/03/19/5aa6066eca4741987d8b456e.html>se
> avecina. El domingo 28 de octubre entra en vigor el horario de invierno 2018 en
> México y en el mundo; la buena noticia es que deberás de atrasar tu reloj una
> hora, ganando sesenta minutos de sueño.
> El cambio se dará durante la madrugada del domingo, por lo que a las 3 AM los
> relojes tendrán que ponerse a las 2 AM. El horario de invierno permanecerá
> vigente hasta el día 7 de abril del 2019.
> I am sorry I cannot still confirm this issue, I have sent an email to Mexico´s
> CETRAM and I am waiting for an official response.
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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