Hello, I'd like to suggest several corrections to past time changes in Mexico. In 1931, the decree implementing DST specified that it would take effect on 30 April, so I suppose that DST started on that date at 0:00. The database currently says 1 May at 23:00. https://www.dof.gob.mx/nota_to_imagen_fs.php?cod_diario=192270&pagina=2&secc... In 1981, the decree changing Campeche, Yucatán and Quintana Roo to UTC-5 specified that it would enter into force on 26 December 1981 at 2:00. The database currently says 23 December 1981, which was the date of publication of the decree. https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4705667&fecha=23/12/198... In 1982, the decree returning Campeche and Yucatán to UTC-6 specified that it would enter into force on 2 November 1982 at 2:00. The database currently says 2 December 1982. https://www.dof.gob.mx/nota_to_imagen_fs.php?cod_diario=205689&pagina=3&secc... Quintana Roo changed to UTC-6 on 4 January 1983 at 0:00, and again to UTC-5 on 26 October 1997 at 2:00. These changes are not currently included in the database. https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4787355&fecha=28/12/198... https://www.dof.gob.mx/nota_to_imagen_fs.php?cod_diario=209559&pagina=15&sec... Durango, Coahuila, Nuevo León and Tamaulipas were set to UTC-7 on 1 January 1922, and changed to UTC-6 on 10 June 1927. Then Durango, Coahuila and Nuevo León (but not Tamaulipas) returned to UTC-7 on 15 November 1930, observed DST in 1931, and changed again to UTC-6 on 1 April 1932. The database currently shows all these states set to UTC-6 on 1 January 1922. https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4441846&fecha=29/12/192... https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4541520&fecha=09/06/192... https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4491963&fecha=15/11/193... https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4418437&fecha=21/01/193... The database currently shows the time change of 10 June 1927 occurring at 23:00 in all time zones that have such change. However, the decree only said 10 June 1927, without specifying a time, so I suppose that it should be considered at 0:00. https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4541520&fecha=09/06/192... In 1942, the decree changing Baja California, Baja California Sur, Sonora, Sinaloa and Nayarit to UTC-7 was published on 24 April, but it said that it would apply from 1 April, so it's unclear when the change actually occurred. The database currently shows 24 April 1942. https://www.dof.gob.mx/nota_to_imagen_fs.php?cod_diario=192203&pagina=2&secc... Baja California Sur, Sonora, Sinaloa and Nayarit never used UTC-8. The database shows these states changing to UTC-8 on 14 January 1949, but this change only occured in Baja California. https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4515613&fecha=13/01/194... In 1945, the decree changing Baja California to UTC-8 specified that it would take effect on the third day from its publication. It was published on 12 November, so it would take effect on 15 November. The database currently says 12 November 1945. https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4555049&fecha=12/11/194... In 1948, the decree changing Baja California to UTC-7 specified that it would take effect on "this date". The decree was made on 13 March, but published on 5 April, so it's unclear when the change actually occurred. The database currently shows 5 April 1948. https://www.dof.gob.mx/nota_to_imagen_fs.php?cod_diario=188624&pagina=2&secc... In 1949, the decree changing Baja California to UTC-8 was published on 13 January, but it said that it would apply from 1 January, so it's unclear when the change actually occurred. The database currently shows 14 January 1949. https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4515613&fecha=13/01/194... Baja California also observed UTC-7 from 1 May to 24 September 1950, from 29 April to 30 September 1951 at 2:00, and from 27 April to 28 September 1952 at 2:00. These changes are not currently included in the database. https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4600403&fecha=29/04/195... https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4623553&fecha=23/09/195... https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4469444&fecha=27/04/195... https://www.dof.gob.mx/nota_to_imagen_fs.php?codnota=4533868&fecha=10/03/195... All changes in Baja California from 1948 to 1952 match those in California, on the same dates or with a difference of one day. So it may be easier to implement these changes as DST with rule CA during this whole period. Regards, David