Timezone Change with date::manip

[marcie]

I'm writing a program which retrieves data from a 3rd party and
inserts it into a sql database. The data provided has timestamps in
GMT and I want to insert them with both the GMT time and Central time.

I've got everything working right now but when happens when daylight
savings ends? Here's my current code.

use Date::Manip;

my $date = &ParseDate("$gmt_datetime");
$cst_datetime = &Date_ConvTZ($date,"GMT","CDT");

Do I have to change my code to use CST when daylight savings ends or
if there someway to work around this.