Update Order Status using Cron Job

Question

I am trying to setup a Cron to automatically update order statuses that have a are in a "Processing" state in Magento.

Here is what I have so far

config.xml

    <orders>
        <schedule><cron_expr>0 9,11,13,15,17 * * *</cron_expr></schedule>
        <!--schedule><cron_expr>*/15 * * * *</cron_expr></schedule-->
        <run><model>orders/Status::cron</model></run>
    </orders>

</jobs>

And inside Status.php

public function updateOrderStatus($order)
{

    $order->setOrderStatus(self::STATUS_PACKING);

    $order->save();

}

What I would like to do is change any orders from "Processing" to "Packing" but I can't seem to find a way to do it...

If anyone knows any good resources please share.