How do I get the timezone form reference on a date field?

Question

In Drupal 7 I have a date field in a content type that has the Time zone handling option set to "Date's time zone". Setting this option will render a drop down list of time zones in your date field.

I am trying to replace the list of core time zones with a smaller list for just the United States. I found this post which works perfectly for overriding the timezone drop down list on the user profile page. However, I have not been able to figure out how to get a reference to the timezone select list on a date field.

The timezone reference on the user profile field is:

 $form['timezone']['timezone']['#options']

If you print the $form variable to the screen you can clearly see the time zones in the above reference.

What I can't figure out is where the timezone options are in the form variable for a date field. I would expect them to be in somewhere in

 $form['field_event_dates']['und'][0]

I do see a default value for the timezone at

 $form['field_event_dates']['und'][0]['#default_value']['timezone']

but I can't find "options" in there.

Any ideas where the "options" for the time zone are set in the form variable?

Answer 1

Use hook_date_timezone_process_alter in your custom module to do the magic, see below example and adapat if for you needs

function MODULENAME_date_timezone_process_alter(&$element, &$form_state, $context) {
  // add some logic here
  // keep only the needed values
  // dsm($element['timezone']['#options']);
  $element['timezone']['#options'] = array(
    'Africa/Abidjan ' => 'Africa/Abidjan',
    'America/Detroit' => 'America/Detroit',
  );
}