- date_default_timezone_set: documentation ( source)
<?php
date_default_timezone_set( 'UTC' );
$tz_p14 = new DateTimeZone( 'Pacific/Kiritimati' );
$date_time = new DateTime( '2014-02-01 00:01:00', $tz_p14 );
echo $date_time->format( "Y-m-d H:i:s\n" );
$tz_m12 = new DateTimeZone( 'Pacific/Samoa' );
$date_time->setTimezone( $tz_m12 );
echo $date_time->format( "Y-m-d H:i:s\n" );