You can use `template_preprocess_node` to alter `submitted` variable. Here is the sample code.

    function awesome_preprocess_node(&$variables) {
      $node = $variables['node'];
      $date = format_date($node->created, 'custom', 'm-d-Y - H:i');
      $variables['submitted'] = t('Submitted by !username on !datetime', array('!username' => $variables['name'], '!datetime' => $date));
    }

The most important line there is `$date = format_date($node->created, 'custom', 'm-d-Y - H:i');`. Change the format (`m-d-Y - H:i`) to any format you want. 

See [this page][1] about PHP date format. 


  [1]: http://php.net/manual/en/datetime.formats.date.php