title: execute crontab twice daily at 00h and 13:30
body: <p>i want to execute a script twice daily at 00:00 and 13:30 so i write :</p>
  
  <pre><code>0,30 0,13 * * *
  </code></pre>
  
  <p>it seems wrong for me, because like this, the script will fire at 00:00 , 00:30 , 13:00 and 13:30. Any idea ?</p>