Mexico revision

Jesper Norgaard Welen jnorgard at
Sun Feb 4 06:02:08 UTC 2007

I have been revising the pages of the Mexican Congress Library at
tm about timezone changes since 1921 which is also mentioned in the
'northamerica' file (although without the HTM file mentioned). The aim is to
bring tz database up-to-date with this information, which is already used as
preferred source to Shanks in the 'northamerica' file. I guess then I don't
have to argue why I think these pages should have more priority, but rather
I would like to point out their deficiencies too before looking at the
actual changes to the tz database that I'm recommending. 

First of all about completeness, I have serious doubt to that these pages
are *all* the official Mexican documents that exist about timezone matters -
especially concerning the gap of no decrees between 1948 and 1981. In fact,
I believe that these decrees are accurate and were followed, but that likely
other decrees have not been included in the list, whether there were 33 year
gaps or they were smaller. About dates, it seems that most decrees only have
a *publication* date, not an effective date. Here is a summary (I named the
decrees A to R to have some reference):

Decree, Official Publish Date, Effective Date
A: 1921-12-20, 1922-01-01 0:00:00
B: 1923-12-00
C: 1927-06-09
D: 1930-11-15
E: 1931-04-28
F: 1932-01-21, 1932-04-01
G: 1942-04-24
H: 1945-11-12
I: 1948-04-05
J: 1981-12-23
K: 1982-11-02
L: 1988-02-17
M: 1989-03-23
N: 1989-03-30
O: 1996-01-04
P: 1997-08-13
Q: 1998-07-31
R: 1999-03-29

the 'northamerica' file states

# Here are the discrepancies between Shanks & Pottenger (S&P) and the MLoC.
# (In all cases we go with the MLoC.)
# S&P report that Baja was at -8:00 in 1922/1923.
# S&P say the 1930 transition in Baja was 1930-11-16.
# S&P report no DST during summer 1931.
# S&P report a transition at 1932-03-30 23:00, not 1932-04-01.

Baja at -8:00 seems unlikely, since decree A only mentions -6:00 and -7:00.
That the 1930 transition in Baja was 1930-11-16 sounds perfectly plausible
to me, I think we should go with Shanks here, and actually it is quite
possible that all changes in Mexico (also America/Mexico_City,
America/Chihuahua, America/Hermosillo, America/Mazatlan, and
America/Tijuana) should be 1930-11-16.
No DST during summer 1931 sounds unlikely, see decree E. However some doubt
does arise since the decree talks about 'every year' and beginning of
April each year, while being published nearly a month later (on 1931-04-28).
A transition at 1932-03-30 23:00, 1 day and 1 hour before the decree F
stated it should be (in fact one of the only Effective Dates of all these
decrees) seems extremely unlikely.

I don't have a copy of Shanks and Pottenger, so I can't make corrections
accordingly. But I think we should believe more in Shanks than these pages
for Effective dates if the changes to timezones (the content) are otherwise

Now to the actual changes. I am attaching a full 'northamerica' file
(version 2007a changed) for convenient difference checking.

# Quintana Roo
Zone America/Cancun	-5:47:04 -	LMT	1922 Jan  1  0:12:56
			-6:00	-	CST	1981 Dec 23
+			-5:00	-	E%sT	1996 Jan  4  0:00
+			-6:00	Mexico	E%sT	1997 Oct 26  2:00
			-5:00	Mexico	E%sT	1998 Aug  2  2:00

That Cancun went from GMT-6 to GMT-5 (no DST involved) at 1981-12-23 is
confirmed in decree J. I'm guessing a little bit above, but we have decree O
saying explicitly that there are three zones, and one is "all of the
national territory except the two other zones". So definitely Cancun most
have been on Mexico City time since this decree took effect (sometime
on/after 1996-01-04). Decree P then introduces Cancun on GMT-4 during DST
and GMT-5 outside, in the end of the DST period defined in decree O. So I
assume a smooth transition where Cancun ended their DST from GMT-6 to GMT-5
by simply not switching back the clock to GMT-6, but continuing with GMT-5
until 1998-04-05 where GMT-4 is introduced (DST).

# Campeche, Yucatan
Zone America/Merida	-5:58:28 -	LMT	1922 Jan  1  0:01:32
			-6:00	-	CST	1981 Dec 23
-			-5:00	-	EST	1982 Dec  2
+			-5:00	-	EST	1982 Nov  2
			-6:00	Mexico	C%sT

Decree K has publication date 1982-11-02. Would the above effective date
1982-12-02 just by a typo of some kind? I don't know what Shanks date is,
but I assume we have nothing better than to go with the publication date.
Correct me if I'm wrong, that is quite possible here.

# Coahuila, Durango, Nuevo Leon, Tamaulipas
Zone America/Monterrey	-6:41:16 -	LMT	1921 Dec 31 23:18:44
+			-7:00	-	MST	1927 Jun 10 23:00
+			-6:00	-	CST	1930 Nov 15
+			-7:00	-	MST	1931 May  1 23:00
+			-6:00	-	CST	1931 Oct
+			-7:00	-	MST	1932 Apr  1
-			-6:00	-	CST	1981 Dec 23
			-6:00	Mexico	CST	1988
			-6:00	US	C%sT	1989
+			-6:00	Mexico	C%sT	2001 Sep 30 02:00
+			-6:00	-	CST	2002 Feb 20
			-6:00	Mexico	C%sT

This set of changes, although looking complicated, are really quite simple.
We have a specific difference for the above four states in decree L of
1988-02-17 applying US style DST in 1988. But there is no evidence that they
were any different than Mexico City before or after that year. In fact
having GMT-6 unaltered since 1922 to 1988 seems to me extremely unlikely,
for instance decree B says that the states from Baja California Sur and
Sonora until Veracruz and Oaxaca (exclusively) are all on GMT-7, while
Veracruz, Tamaulipas and Oaxaca (and presumably states to the south and east
of those) are on GMT-6. Tamaulipas then consists of an exception here, but
since this happened before the cutoff date of 1970, we don't need a new
timezone for Tamaulipas.

Note that I copy the two lines for years 2001-2002 from the
America/Mexico_City timezone, although I don't understand them - what is the
difference to just using the last line e.g. GMT-6 with Mexico rule, since

# Baja California
Zone America/Tijuana	-7:48:04 -	LMT	1922 Jan  1  0:11:56
			-7:00	-	MST	1924
			-8:00	-	PST	1927 Jun 10 23:00
-			-7:00	-	MST	1930 Nov 15
+			-7:00	-	MST	1930 Nov 16
-			-8:00	-	PST	1931 Apr  1
+			-8:00	-	PST	1931 May  1 23:00
-			-8:00	1:00	PDT	1931 Sep 30
+			-8:00	1:00	PDT	1931 Oct
			-8:00	-	PST	1942 Apr 24

First I change effective date from 1930-11-15 to 1930-11-16 as per Shanks in
the note above. Then I revert the effective date 1931-04-01 to 1931-05-01
23:00 as in the other timezones, because I think it is unlikely that the
change happened before the decree E about the change was published
(1931-04-28). Also I think this was set as Apr 1 because that is the date
that was specified in the decree E, but for all years, not just 1931.
September 30 is quite likely also a misinterpretation of the original decree
E. It states that every year DST runs from 1.April till of September,
but that winter time runs from 1.October to of March. Clearly what is
meant is 1930-09-30 24:00 and not 1930-09-30 0:00, or rather 1930-10-01

Note there is a typo in a note from Debra Goldsmith where 2:OO should be
2:00, above the Indiana definition.

I'm not so happy with the Reuter transcript, quite possibly produced in a
hurry in Reuters just around the date of the actual event:

# From Reuters (2001-09-04):
# Mexico's Supreme Court on Tuesday declared that daylight savings was
# unconstitutional in Mexico City, creating the possibility the
# capital will be in a different time zone from the rest of the nation
# next year....  The Supreme Court's ruling takes effect at 2:00
# a.m. (0800 GMT) on Sept. 30, when Mexico is scheduled to revert to
# standard time. "This is so residents of the Federal District are not
# subject to unexpected time changes," a statement from the court said.

The note about the Supreme Court reinstating the DST rules already
established by the president, is amusing but perhaps not too relevant. But
that the Supreme Court declared daylight saving (not daylight saving*s*)
unconstitutional, is plain wrong. Here is a better source (my translation):

======= Start of translation =======
The first of February 2001 was published in the official newspaper of the
federation the presidential decree to establish DST from the First Sunday of
May till the Last Sunday of September (five months) in all of the national
territory ...

Supported by a telephone inquiry of the and of February 2001,
where 239,437 inhabitants of Mexico City where asked their opinion, the
mayor of the capital emitted a decree the of February, defining that
the capital would not implement DST.

Additionally, the of March 2001 the mayor put forward a constitutional
dispute about the validity of the presidential decree published the of
February 2001.

It was the of September 2001 that the Supreme Court decided that it
was the responsibility of the Congress to determine laws about GMT offset
and DST.

Congress then approved the current law of DST published in the Official
Newspaper of December 2001.

Finally the of March 2002 was published the law about DST during 7
months which is applied each year in Mexico.
======= End of translation =======

In short, the presidential decree was deemed unconstitutional, not daylight
saving. Something not mentioned above was that the mayor's decree about
setting the time for the capital, was also deemed unconstitutional, in
effect a "draw" between the two combattants - it was all about power, of
course. The presidential decrees had been a tradition since 1917. But an
unconstitutional one, it seems.

- Jesper Nørgaard Welen

-------------- next part --------------
A non-text attachment was scrubbed...
Name: northamerica
Type: application/octet-stream
Size: 102726 bytes
Desc: not available
Url : 

More information about the tz mailing list