UNIX timestamp a string From http://stackoverflow.com/questions/10040291/converting-a-unix-timestamp-to-formatted-date-string, http://stackoverflow.com/questions/5710275/last-week-this-week-php
<?php
$timestamp = strtotime('last week');
echo gmdate("Y-m-d\TH:i:s\Z", $timestamp) . '<br>';
echo 'Semana pasada: '.date('Y-m-d H:i:s',strtotime("-7 days"));
?>