The Time Zone Act, published in the DOF on 29 December 2001, sets the official time at a specific point in the national territory, depending on the geographical location. It also defines time zones and how the time in each zone is related to the time of the prime meridian. It should be noted that prime meridian time is determined by the time scale called Coordinated Universal Time, UTC. It should be noted that the UTC time scale is generated by the International Bureau of Weights and Measures (BIPM), is a time scale for scientific purposes and is virtual (there is no physical signal associated with this scale). In Mexico, the physical realization of UTC is responsible for the National Center of Metrology, called UTC (CNM). The creation of the Cagigal Observatory in 1888, in addition to the beginning of the development of the first technical institutions of a public nature in the Republic, entailed the imperative need to define a temporal model that clearly and solely regulates the measurement of time, so that it can be disseminated through the media available for the time. Thus, from 1912, after adopting the meridian of Villa de Cura (67° 30` west longitude) as the first geographical reference for a national time system, the HLV began to provide the Central Office of National Telegraphs with astronomical determinations of local time. where N is 6 hours for winter time and 5 hours for daylight saving time. Daylight saving time applies from the first Sunday in April at 2:00 a.m. until the last Sunday in October at 2:00 a.m.

In 1939, tests began on the transmission of time by two radio stations with national coverage: Radio Broadcasting Caracas and Radio Difusora Venezuela, which assumed mechanisms of temporal synchronization with the HLV service using telegraph systems, while the procedures for determining and adjusting local and sidereal time remained almost intact until the 1950s. In 1959, the installation of the first quartz watches of unprecedented precision for the time began (a second error every 30 years), whose absolute calibration was systematically carried out from astronomical observations of selected stars. This true “quantum technological leap” was completed by the integration of an automatic announcement of the time by telephone and the inauguration of the standard frequency service for technical applications. The legal time of each country is represented in local time scales, NMIs or designated laboratories in the order of time and frequency that have demonstrated their technical competence are approved to contribute to the international time scale called Coordinated Universal Time – UTC, Colombia has been contributing to this time scale since 2017. National territory (with the exception of the border strip with the United States of America, Quintana Roo and Sonora) In the national territory, with the exception of the border strip with the United States of America and the states of Quintana Roo and Sonora, daylight saving time begins on the first Sunday of April at 2:00 a.m., at which time the clocks are advanced by one hour. and ends on the last Sunday of October at 2:00 am, when the clocks are set back an hour. For the current year 2022, daylight saving time on the national territory (with the exception of the border strip with the United States of America) begins on Sunday, April 3 and ends on Sunday, October 30. Example of official time zone in winter, summer and border strip NOTE: In accordance with section IV of Article 3 of the Time System Act in the United Mexican States, islands, reefs and bays are included in the meridian corresponding to their geographical location and in accordance with accepted instruments of international law.

The states of Quintana Roo and Sonora do not provide for daylight saving time.