[tz] timezone history of Uruguay

Tim Parenti tim at timtimeonline.com
Fri Feb 16 03:27:26 UTC 2018

I must admit, over the last fortnight, I did a bit more spelunking into the
depths of Uruguayan law than I was initially expecting.  The result is the
attached proposed patch.

The records were actually quite accessible, and typically straightforward
to transcribe and translate.  Although the dates listed in Almanaque 2018
correspond to when the various laws and decrees were made, they were
typically published in the Diario Oficial some time later.  Since the
changes were generally promulgated on short notice, such publication often
occurred after the changes took effect.  But at least the Almanaque, or its
primary sources, did a good job of compiling references to all the various
laws and decrees.  In general, even with a limited understanding of
Spanish, simply looking for "hora legal" in the index summaries of each
day's Diario in the online archives <http://www.impo.com.uy/diariooficial/>
made it fairly easy to find the documents I looked for.

Of course, there are nearly 50 such documents from the last 110 years that
are referenced by the Almanaque in its compilation.  Although I did not
independently verify every single one of these, there is sufficient context
in the oldest and newest ones to suggest that most, if not all, transitions
prior to 2005 were at midnight.  Additionally, the vast majority of the
dates given by Almanaque are Sundays, so Sunday 00:00 transitions are
generally assumed as correct, as this is consistent with early laws as well
as much of what we already had.  There are, however, a few exceptions where
Almanaque listed a Saturday or a Monday instead; in these cases, the
relevant legal documents do, in fact, confirm those dates.  Details are
given in the proposed commentary changes to southamerica.  A few typos in
Almanaque's compilation (and, though I don't mention them, even in some
early laws!) were also uncovered, but the references were solid enough that
reasonable confidence could be established in the data presented in the

Unsurprisingly, it turns out that most of the original data from Shanks &
Pottenger is easily refutable.  This results in significant changes to
timestamps prior to 1991, which are detailed a bit more in the proposed
additions to NEWS.  Of particular note, there were four different offsets
during the calendar year 1974, rendered as four different DST amounts (0,
30, 60, and 90 minutes, though not in that order).

Tim Parenti
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