Cakephp: record random once a day

how can I have random results that change only after 24 hours?

 $random = $this->Post->find('first',array(
        'conditions' => array(
            'Post.active'=>1,
        ),
        'order' => 'rand()',
    ));
    $this->view($random['Post']['id']);
    $this->render('view');