Pourquoi ne pas simplement le convertir en UTC ?
$datetime = "2010-01-19 00:00:00";
echo "Datetime Before: ".$datetime."<br />";
$dttostr = strtotime("2010-01-19 00:00:00");
echo "Datetime After: ".formatToUTC($dttostr)."<br />";
echo "System Timezone: ".date_default_timezone_get()."<br />";
function formatToUTC($passeddt) {
// Get the default timezone
$default_tz = date_default_timezone_get();
// Set timezone to UTC
date_default_timezone_set("UTC");
// convert datetime into UTC
$utc_format = date("Y-m-d\TG:i:s\Z", $passeddt);
// Might not need to set back to the default but did just in case
date_default_timezone_set($default_tz);
return $utc_format;
}