New Cron Entry... Super lost.

Hey guys, I was looking at the Trophy Check cron job, and I wanted to write one that would make a user that has been registered over 3 days get put into a certain group. Any help with this?

This is what I fiddled out. I have no way to debug this other than trial and error.

* Cron entry for trial checking
* @package XenForo_Trial
class XenForo_CronEntry_Trial
    * Runs the cron-based check for trial termination
    public static function runTrialCheck()
        /* @var $userModel XenForo_Model_User */
        $userModel = XenForo_Model::create('XenForo_Model_User');

// Assuming that 13 is the group number for your trial members
// Assuming that 'timeinseconds' is a real number

        $users = $userModel->getUsers(array(
            'secondary_goup_ids' => 13,
            'register_date' => array('>', XenForo_Application::$time - timeinseconds)

        foreach ($users AS $user)
// Not too sure on how to set fields...
            $user['secondary_group_ids'] = null;


foreach ($users AS $user){
$dw = XenForo_DataWriter::create('XenForo_DataWriter_User');