Daylight saving time will be in effect from 2008-10-19 00:00 to 2009-03-15 00:00 in those provinces that choose to observe it. The presidential decree to that effect was published in the Boletín Oficial  for 2008-10-17. I haven't yet incorporated this information in the tables below.

Argentina passed legislation implementing Daylight Saving Time nationwide from 2007-12-30 00:00 to 2008-03-16 00:00. The text of the law is in the Boletín Oficial  for 2007-12-28. The law provides that the Executive Branch will set the dates for the beginning and end of DST in subsequent years. It also sets up a study commission. The Executive Branch is authorized to change the time zones based on the outcome of the study, "in the entire national territory or according to its east-west geographical position" (my translation from the Spanish). In other words, the country could be split into two or more time zones again, depending on the executive decision.

San Luis province changed from UTC-2:00 to UTC-3:00 as of 2008-01-21 00:00 local time, ending daylight saving prematurely in that province.

Events in 2004

Argentina had been united in observing UTC-3:00, without DST, since 2000-03-03. In autumn (Southern hemisphere) 2004, a number of provinces set their clocks back an hour, effectively moving to the next time zone westward, with the intention of observing DST next spring. Another way to express it is that those provinces went on reverse DST: instead of turning the clocks ahead in the summer, they would turn the clocks back in the winter. However, some software is written with the assumption that DST is always an hour later than standard time, so it's best to use the first description.

Mendoza returned to UTC-3:00 on 2004-09-26. San Juan set its clocks back on 2004-05-31, and set them forward again on 2004-07-25. Tucumán returned to UTC-3:00 on Sunday morning, 2004-06-13. Tucumán had not observed the energy savings that the time change was intended to produce. Tierra del Fuego, through a "normative error", set its clocks back to UTC-4:00 on Sunday, 2004-05-30. Catamarca, Chubut, La Rioja, Santa Cruz, and Tierra del Fuego reverted to UTC-3:00 on 2004-06-20.

Rules currently in force

Argentina's time is UTC-3 during local winter, and UTC-2 during local summer. The duration of the summer period for this year is 2007-12-30 00:00 to 2008-03-16 00:00. Subsequent years will be announced at a suitable date.

Time zone history

Source: This information was adapted from the tz database. Zone names come from that database. The names don't necessarily match any names used in the "real world".

For dates in 2004, use this table.

Locations in Argentina observed Local Mean Time until 1894-10-31 00:00 (as measured after the transition). At that moment, the entire country synchronized on Córdoba's Local Mean Time, which was UTC-4:16:48. The next transition occurred at 1920-05-01 00:00, when clocks were set ahead sixteen minutes and forty-eight seconds to be an even UTC-4. Argentina remained unified on UTC-4 until its first daylight saving time was inaugurated in 1931. To convert dates and times since then to UTC, follow the steps below.

Time zone names

The tz database has arbitrarily designated the abbreviations ART, ARST, WART, and WARST for [Western] Argentine [Summer] Time. The Zone Names listed above are also arbitrary identifiers from the tz database. Current news articles describe the UTC-4 zone as "hora cordillerana", which could be translated "Andes Time".