TZ has for Colombia a single period with time zone 4h west. # Rule NAME FROM TO - IN ON AT SAVE LETTER/S Rule CO 1992 only - May 3 0:00 1:00 - Rule CO 1993 only - Apr 4 0:00 0 - I think the end date 4 April is wrong, it should be 6 February 24h or 7 February 0h The time shift was called Hora Gaviria, and caused by shortage of electricity in connection with El Niño . Source: *DECRETO 267 DE 1993 * https://www.suin-juriscol.gov.co/viewDocument.asp?ruta=Decretos/1061335 *Artículo 1° *Adoptar como hora legal en el territorio de la República, la del Tiempo Universal Coordinado, UTC, disminuido en cinco (5) horas. *Artículo 2° *El cambio de hora se hará efectivo a las veinticuatro horas del día 6 de febrero del presente año. There is also a newspaper article https://www.eltiempo.com/archivo/documento/MAM-32922 of 4 feb 1993, but the text is less clear to my limited understanding of Spanish. See also https://es.wikipedia.org/wiki/Crisis_energ%C3%A9tica_de_1992_en_Colombia **