The first official standardization took place on 1894-08-01, when a decree regulated the time for national railroads.
The official time switched between UTC-4 and UTC-3 from 1920 to 1969, and then between UTC-3 and UTC-2 from 1974 to 1993. On 1993-03-07 it was fixed at UTC-3.
In the tz-database Argentina has the following zones:
America/Argentina/Buenos_Aires - Buenos Aires (BA, CF)