The reason is that I'm doing timezone conversion. The code is supposed to be high-availability ... it is very bad if times get snookered even a couple times a year.

I'm using Date::Manip to perform the conversion. Date::Manip understands MST and MDT, but it does not understand something like MST7MDT. For example,

#!/usr/bin/perl
use strict;
use Date::Manip;
my $date = &ParseDate("2002-05-29 08:00:00");
print "The unconverted date is [".&UnixDate($date,"%Y-%m-%d %H:%M:%S")
+."]\n";
my $from = 'MDT';
my $to = 'GMT';
my $converted = &Date_ConvTZ($date,$from,$to);
print "The conversion from [$from] resulted in [".&UnixDate($converted
+,"%Y-%m-%d %H:%M:%S")."]\n";
$from = 'MST7MDT';
$converted = &Date_ConvTZ($date,$from,$to);
print "The conversion from [$from] resulted in [".&UnixDate($converted
+,"%Y-%m-%d %H:%M:%S")."]\n";
[download]

The unconverted date is [2002-05-29 08:00:00]
The conversion from [MDT] resulted in [2002-05-29 14:00:00]
The conversion from [MST7MDT] resulted in [2002-05-29 08:00:00]
[download]

So I need to know whether a given date is in Mountain Daylight Time or Mountain Standard Time.

Edit by tye to change PRE tags to CODE tags