update magento currency via cron or simple php script

update_currency.php

<?php 
include("app/Mage.php");
Mage::app();
$now = new \DateTime();
echo "start downloading rates : {$now->format("Y-m-d H:i:s")}\n";
$model = Mage::getModel("directory/currency");
$currency_converter= Mage::getModel("directory/currency_import_webservicex");
$rates = $currency_converter->fetchRates();
echo json_encode($rates) . "\n";
echo "has been downloaded\n";
echo "start saving rates to db \n";
$model->saveRates($rates);
$finished = new \DateTime();
echo "finsihed saving rates to db on : {$finished->format("Y-m-d H:i:s")} \n";