How can I add the +0430 timezone to Drupal 6?
I think this looks like a problem in PHP. The timezone is being used by the Date module, and that contains date_timezone_abbr(), which uses PHP's timezone_abbreviations_list(). 

Only the keys are stored, and the PHP function is being used. I am afraid there is no way out of this, unless there is a way to convince PHP.

When I tried the following code, I get 4, not 4.5.

$a = timezone_abbreviations_list();
echo $a['aft'][0]['offset'] / 3600;