Comparison between two dates does not work correctly
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I just want to compare two dates : the system date and the one registered into my SQL database. When I compare only the date like below :

    $this->ArgusArticle->find('all', array(
       'conditions' => array('ArgusArticle.visible' => true,
       'ArgusArticle.publication_date <= ' => date('Y-m-d')), <--
       'order' => 'ArgusArticle.id DESC',
       'limit' => 3
    ));

it works perfectly ! But if I add "H:i" to check the time it's not good!

    $this->ArgusArticle->find('all', array(
       'conditions' => array('ArgusArticle.visible' => true,
       'ArgusArticle.publication_date <= ' => date('Y-m-d H:i')), <--
       'order' => 'ArgusArticle.id DESC',
       'limit' => 3
    ));

In my database the date and time is registered like this : 2012-07-31 15:45 (for example)
I work on cakephp framework and the type of my data is datetime.
Thanks in advance for your help.