Abolished in 2022
Mexico ended horario de verano nationwide on 30 October 2022, when the Ley de los Husos Horarios came into force. Almost the entire country now stays on standard time all year. If you are working from a guide written before 2023, or software with an out-of-date timezone database, it will be wrong by an hour for part of the year.
The border exception
A strip of municipalities along the United States frontier still observes daylight saving, specifically so that cross-border commerce, commuting and school runs are not thrown out by an hour twice a year. Baja California observes it statewide, in step with US Pacific Time. Individual municipalities in Tamaulipas, Nuevo León, Coahuila and Chihuahua — Tijuana, Ciudad Juárez, Reynosa, Matamoros, Nuevo Laredo, Piedras Negras and others — follow the US schedule of the second Sunday in March to the first Sunday in November.
Earlier opt-outs
Two regions had already left before the national repeal. Sonora dropped daylight saving in 1998 to stay aligned with Arizona, which does not observe it. Quintana Roo, which contains Cancún and the Riviera Maya, left in 2015 when it moved to UTC-05:00 year round to give its tourist economy more usable evening daylight.