The only way to do this is to change the `$node->title` on the loaded object for the webform.  That filename uses that title, so I am assuming you have a webform title of "Localhost Worklog".

The problem with that is you only want to change the node title, when you are downloading the webform (or atleast running through that process).

You have two options (I think).  You could implement a `hook_node_load()` function and then check if the URL is

node/%webform_menu/webform-results/download
**or**

node/%webform_menu/webform-results/download-file

    function MYMODULE_entity_load($entities, $type) {
      if (arg(2) == 'webform-results' && (arg(3) == 'download' || arg(3) == 'download-file')) {
        foreach ($entities as $entity) {
          $entity->title = $entity->title .'_'. now();
        }
      }
    }

[Docs][1]

The other way I can think of is altering the page callback with a `hook_menu_alter()`, changing the title there and then calling their function to return the form or download file with the updated node object to include the time appended to the title.

  [1]: https://api.drupal.org/api/drupal/modules!system!system.api.php/function/hook_entity_load/7.x