Time in Mexico
Mexico uses four main time zones as of February 2015.  Most of the country observes Daylight Saving Time (DST).

  ('Southeast Zone') covers the state of Quintana Roo is UTC−05:00 year round. It is the equivalent of U.S. Eastern Standard Time.
  ('Central Zone') covers the eastern three-fourths of Mexico, including Mexico City, Guadalajara, and Monterrey. For most of the year, it is the equivalent of U.S. Central Time.
  ('Pacific Zone') covers the states of Baja California Sur, Chihuahua, Nayarit, Sinaloa, and Sonora. For most of the year, it is the equivalent of U.S. Mountain Time. The state of Sonora, like the adjacent U.S. state of Arizona, does not observe DST.
  ('Northwest Zone') covers the state of Baja California. It is identical to U.S. Pacific Time, including the DST schedule.

For economic reasons, some metropolitan areas next to the U.S. border follow the U.S. Daylight Saving Time schedule instead of the Mexican schedule, resulting in those areas being an hour off from the rest of their respective states for a few weeks out of the year.

Mexican law dictates that all remote island territories (Guadalupe Island and the Revillagigedo Islands) fall within the time zone corresponding to their geographic location.

History
Standard time was first defined in Mexico in 1922, when President Álvaro Obregón decreed two time zones.  One time zone designated for 90° W (6 hours behind GMT) covered the states of Tabasco, Chiapas, Campeche, Yucatán, and Quintana Roo. A second time zone designated for 105° W (7 hours behind GMT) covered the rest of the country, from Baja California to Veracruz and Oaxaca.

In 1930 three zones were decreed: Hora del Oeste (120° W, UTC−08:00) for the state of Baja California (norte); Hora del Golfo (90° W, UTC−06:00) covering the states of Tamaulipas, Veracruz, Oaxaca, Tabasco, Chiapas, Campeche, Yucatán and Quintana Roo; and Hora del Centro (105° W, UTC−07:00) for the rest of the country.

It was decreed in 1942 that the Hora del Noroeste (105° W, UTC−07:00) should cover only the states of Baja California Sur, Sonora, Sinaloa, and Nayarit; while the Hora del Centro (90° W, UTC−06:00) was used for the rest of the country.

The time zone Hora del Sureste (75° W, UTC−05:00) was created for tourist reasons in 1981, originally covering the states of Campeche, Yucatán, and Quintana Roo. The three states returned one year later to the Hora del Centro (90° W, UTC−06:00);  Quintana Roo, however, returned to the Hora del Sureste (75° W, UTC−05:00) from October 1997 to August 1998 and then again in February 2015.

Daylight saving time

The first observation of DST was in 1931, but only for the state of Baja California. It used the "Hora del Centro" from April 1 to September 30, and the "Hora del Oeste" the rest of the year. Until 1996, Baja California was the only Mexican state to officially observe DST every year, coinciding with the observance of DST across the border in San Diego, California. In addition to that, the states of Durango, Coahuila, Nuevo León and Tamaulipas unofficially observed DST in 1988 as an experiment, starting on the first Sunday in April and ending on the last Sunday in October. These states abandoned DST the following year and did not return to it until DST was adopted nationwide.

Daylight saving time has been observed nationwide in Mexico since 1996. For municipalities located less than 20 km from the US border, such as Ciudad Juárez, and the entire state of Baja California, it coincides with the longer extended daylight saving period adopted for 2007 in the United States.  But in the rest of the country, daylight saving time is observed between 2 a.m. on the first Sunday in April through 2 a.m. on the last Sunday in October. Quintana Roo and Sonora do not observe DST.

As the United States starts DST on the second Sunday in March and ends it on the first Sunday in November, Mexico's time zones are out of synchronization with American and Canadian time zones for two periods each year. The first is the three or four  weeks between the second Sunday in March and the first Sunday in April. The second is the single week between the last Sunday in October and the first Sunday in November.  During these periods, clocks in Mexico City match those in Denver rather than those in Chicago.  The Mexican Stock Exchange changes its hours during these periods in order to maintain synchronization with the U.S. markets. Conversely, television schedules are not changed for these situations, meaning Mexican television networks which are carried directly by American cable and satellite services have their programming aired an hour behind in the United States during these interregnums.

In 1998, the state of Chihuahua moved from Central time to Mountain time.  This is likely because Ciudad Juárez is directly across the border from El Paso, Texas, which is on Mountain Time.  Later, in 2001, Mexico experimented with a shorter daylight saving period from the first Sunday in May to the last Sunday in September, returning to the previous seven-month schedule in 2002. Nevertheless, since Mexico City and other southern states decided to use again the shorter five-month daylight saving period in 2002, the Mexican Congress ruled that this decision was a federal one, and so it has to be ruled by the same congress. This decision backfired when the United States extended their DST period in 2007, because the Mexican Congress now refused to do the same for Mexico, under the strong influence of the southern states representatives. Two years later, the population of the northern border cities complained about the time difference between those cities and their US counterparts and their government requested the DST extension again. For the second time, Congress refused to adopt it nationwide. As a result, only the areas within 20 km of the United States border, as well as all of Baja California, began observing DST on the US schedule in 2010, while the rest of the country retained the pre-2007 United States DST schedule. A new bill was proposed in September 2015 for the rest of the country to also observe DST on the extended 2007 US schedule, thus eliminating the distinction between the border cities and the rest of Mexico. Congress refused to approve the change for the third time in a 10-year period, discarding the bill on June 29, 2016.

Daylight saving time is observed in all parts of the country except for the states of Quintana Roo, and Sonora, which decided to remain on standard time beginning in 1999. For Sonora, which shares its northern border with Arizona, this is to coincide with the non-observation in Arizona. The island territories do not currently observe daylight time either. During non-DST period, Mexico uses four different time zones.

IANA time zone database
Data for Mexico from zone.tab in the IANA time zone database.

See also
Effects of time zones on North American broadcasting

References

External links