title: Finding out when an order status has been set to completed
body: <p>I'm selling virtual products in my store where my customers buy a subscription for sth. This subscription is valid for 31 days beginning with the day when the order has been completed.</p>
  
  <p>How do I find out the day when the order status had been set to completed?</p>
  
  <p>My Idea was to look for the "updated_at" field of an order but I'm unsure if this is the right way to determine when the order was completed.</p>
  
  <pre><code>$sales_model = Mage::getModel("sales/order");
  $all_orders  = $sales_model -&gt; getCollection()
                  -&gt;addFieldToFilter('status', 'complete')
                  -&gt;addAttributeToFilter('updated_at', array(
                      'from' =&gt; $one_month_ago,
                      'to' =&gt; date('Y-m-d 24:00:00'),
                      'date' =&gt; true,
                      )
                  );
  </code></pre>