Default expiring date

Have you tried using hook_form_alter? That way, you can modify the form or its fields, and add any custom logic.

You will most likely need to add a validator function, and do checks in there. Something like this:

// Implements hook_form_FORM_ID_alter().
function my_module_form_user_profile_form_alter(&$form, $form_state) {
   $form['#validate'][] = 'my_module_expiration_validate';
 }

// Validator callback
function my_module_expiration_validate($form, &$form_state) {
  // Check if you can accept the value in $form_state['values']['access_code_expiration']
  // If not, call form_set_error('access_code_expiration', $message);
}

I've incorporated this into my patch against issue #2265509:
https://drupal.org/node/2265509

That patch adds functionality to allow you to set a default expiration interval from a module configuration page. Once set, the expiration will default to an interval into the future that you define.

This feature has been added in the latest release.

Verified. Closed.