Udenlands host. Tidszone problem?

function getTimeZoneDateTime($GMT, $timestamp) {
    $timezones = array(
        '-12'=>'Pacific/Kwajalein',
        '-11'=>'Pacific/Samoa',
        '-10'=>'Pacific/Honolulu',
        '-9'=>'America/Juneau',
        '-8'=>'America/Los_Angeles',
        '-7'=>'America/Denver',
        '-6'=>'America/Mexico_City',
        '-5'=>'America/New_York',
        '-4'=>'America/Caracas',
        '-3.5'=>'America/St_Johns',
        '-3'=>'America/Argentina/Buenos_Aires',
        '-2'=>'Atlantic/Azores',// no cities here so just picking an hour ahead
        '-1'=>'Atlantic/Azores',
        '0'=>'Europe/London',
        '1'=>'Europe/Paris',
        '2'=>'Europe/Helsinki',
        '3'=>'Europe/Moscow',
        '3.5'=>'Asia/Tehran',
        '4'=>'Asia/Baku',
        '4.5'=>'Asia/Kabul',
        '5'=>'Asia/Karachi',
        '5.5'=>'Asia/Calcutta',
        '6'=>'Asia/Colombo',
        '7'=>'Asia/Bangkok',
        '8'=>'Asia/Singapore',
        '9'=>'Asia/Tokyo',
        '9.5'=>'Australia/Darwin',
        '10'=>'Pacific/Guam',
        '11'=>'Asia/Magadan',
        '12'=>'Asia/Kamchatka'
    );
    date_default_timezone_set($timezones[$GMT]); //ensures that whenever i return this date, i will get central time
    if ($GMT == -2) $timestamp -= 3600; //since i set that an hour ahead, im subtracting the extra hour now
    return date('Y-m-d H:i:s', $timestamp);
}

var d = new Date()
var gmtHours = -d.getTimezoneOffset()/60;