San Luis time zone history
The San Luis zone has changed its standard time 8 times since 1970, tied second-most among all 312 zones. Daylight saving time was used in 10 years since 1970, last in 2009; under the current rules the clocks no longer change.
UTC−3
Standard time is UTC−3 all year under the current rules.
Summer time in 10 of 57 years since 1970
Before 1970
Standard time changes
| Date | Change | New standard time | Clock label |
|---|---|---|---|
| Before 1970 | |||
| October 31, 1894 | Local mean time (UTC−4:25:24) replaced | UTC−4:16:48 | CMT |
| May 1, 1920 | Standard time forward 17 minutes | UTC−4 | numeric only |
| October 5, 1969 | Standard time forward 1 hour | UTC−3 | numeric only |
| Since 1970 | |||
| March 14, 1990 | Standard time back 1 hour | UTC−4 | numeric only |
| June 1, 1991 | Standard time forward 1 hour | UTC−3 | numeric only |
| October 3, 1999 | Summer offset kept as standard time; clocks did not move | UTC−4 | numeric only |
| March 3, 2000 | Summer offset kept as standard time; clocks did not move | UTC−3 | numeric only |
| May 31, 2004 | Standard time back 1 hour | UTC−4 | numeric only |
| July 25, 2004 | Standard time forward 1 hour | UTC−3 | numeric only |
| January 21, 2008 | Standard time back 1 hour | UTC−4 | numeric only |
| October 11, 2009 | Standard time forward 1 hour | UTC−3 | numeric only |
Daylight saving periods
| Years | Clocks go forward | Clocks go back | Shift and labels |
|---|---|---|---|
| Before 1970 | |||
| 1930 | December 1 | not that year | 1 hour |
| 1931 | October 15 | April 1 | 1 hour |
| 1932–1939 | 1 November, 00:00 | 1 March, 00:00 | 1 hour |
| 1940 | July 1 | March 1 | 1 hour |
| 1941 | October 15 | June 15 | 1 hour |
| 1943 | October 15 | August 1 | 1 hour |
| 1946 | October 1 | March 1 | 1 hour |
| 1963 | December 15 | October 1 | 1 hour |
| 1964–1966 | 15 October, 00:00 | 1 March, 00:00 | 1 hour |
| 1967–1968 | first Sunday in October, 00:00 | first Sunday in April, 00:00 | 1 hour |
| 1969 | not that year | April 6 | 1 hour |
| Since 1970 | |||
| 1974 | January 23 | May 1 | 1 hour |
| 1988 | December 1 | not that year | 1 hour |
| 1989 | October 15 | March 5 | 1 hour |
| 1990 | October 15 | not that year | 1 hour |
| 1991 | not that year | March 1 | 1 hour |
| 2007 | December 30 | not that year | 1 hour |
| 2008 | October 12 | March 9 | 1 hour |
| 2009 | not that year | March 8 | 1 hour |
Also on UTC−3
Mendoza (Argentina), San Juan (Argentina), Cordoba (Argentina), La Rioja (Argentina), Catamarca (Argentina), Tucumán (Argentina), Buenos Aires (Argentina), Uruguay, Salta (Argentina) and Jujuy (Argentina) (nearest first; 19 more on the list of offsets).
Clocks next door since 1970
- Mendoza (235 km): same time except 1,070 days in 1990–1993, 2004, 2008 and 2009.
- San Juan (284 km): same time except 1,136 days in 1990–1993, 2008 and 2009.
- Cordoba (295 km): same time except 1,449 days in 1990–1993, 2004, 2008 and 2009.
- Santiago (Chile) (401 km): same time except 10,245 days in 1970–2014 and 2016–2026; 1 hour behind today.
- La Rioja (434 km): same time except 1,172 days in 1990–1993, 2004, 2008 and 2009.
How it compares
On standard time, clocks in San Luis run 1 hour 25 minutes ahead of local mean solar time.