Time Zone change for San Luis, Argentina

Jesper Nørgaard jnorgard at prodigy.net.mx
Mon Mar 16 18:45:41 UTC 2009

Norberto Nazabal wrote:

>Basically the law says:

>1) We will use the time zone GMT-3 from the 0 hour of the second Sunday of
October to the 24 hours of the second Saturday of April.

>2) We will use the time zone GMT-4 from the 0 hour of the second Sunday of
April to the 24 hours of the second Saturday of October.

I agree that this is an accurate translation of the document which was
published already back in December 2008. However this definition contains
serious problems of consistency. And not only that, if this was published so
long back (2-3 months) why was it not followed in 2009, but rather following
the Chile DST and Buenos Aires Argentinian DST instead with a frantic press
conference the Thursday before the weekend when it was implemented?

The problem of consistency is the perhaps not obvious fact that the Second
Saturday of a month at 24:00 is *not* always the same time as the Second
Sunday at 0:00 of a month. Thus the above definition is not always defining
two contiguous periods (DST and non-DST) as one might think. I am sure this
is an attempt to give an intuitive definition where one period goes to the
24:00 hours of one day, and is replaced with a new period starting at 0:00
hour the next day, but it fails. The first problem will occur in 2012 where
the Second Saturday is 14.th. of April while the Second Sunday is the 8.th.
of April (e.g. the problem occurs when the first in the month is a Sunday).
So literally the definition will have it that GMT-3 will be followed from
2011-10-09 00:00:00 to 2012-04-14 24:00:00 and GMT-4 will be followed from
2012-04-08 00:00:00 : During a week we have both GMT-3 and GMT-4 ??

The most probable scenarios are that either San Luis redefines the decree in
a consistent way, or that either Chile DST or Argentina DST is followed. The
future will tell. Already in October 2009 the two latter are different,
Chile starts DST 2009-10-11 00:00:00 and Buenos Aires starts DST 2009-10-18

Regards, Jesper Nørgaard Welen

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