Actually I don't think the statement (that parent's code will produce an incorrect time during DST) is correct but neither do I think Robin's surmise that the code in Re: How to convert time from one time zone to another will "work on Windows" is universally correct. Under Windows7:

#!/usr/bin/perl
use 5.014;
# convert TZ 

say "\$ENV{TZ}: $ENV{TZ}";     # var had to be manually added on stock
+ W7


{
    local $ENV{TZ} = "EST+05";
    say "In New York, it is " . localtime();
}

{
    local $ENV{TZ} = "IST-05:30";                  # does not return c
+orrect time on W7
    say "In Mumbai, it is " . localtime();         # but, rather, same
+ as NY localtime
}
[download]

outputs:

$ENV{TZ}: EST5EDT                            # TZ is set but this does
+ 
                                             # not appear to be defaul
+t (for Win7)
In New York, it is Mon Apr  2 10:41:23 2012  # correct
In Mumbai, it is Mon Apr  2 10:41:23 2012    #obviously wrong
[download]

But this may be the result of a misconception on my part about 'doze ENV and its vars.
    Anyone care to explicate?