Time Optional using the date_popup type Is there a way to have date/time fields with the date_popup type, but have the time field be something optional for the user to fill in?

I have the UI with both a Date and Time field with the following code:

$form['mygsb_settings']["publish_on_start_date"] = array(
    '#type' =&gt; 'date_popup',
    '#title' =&gt; "Publish Start Date",
);


But when a user doesn't enter the start time, I get back the following validation error from drupal.

The value input for field Publish Start Date is invalid:
The value 2012-03-14 does not match the expected format.

Is there any way to avoid this validation error? Basically, I want to make the time field optional.

Greg
I needed to allow users to give either a datetime or just a date, so I needed to override the default date_popup behaviour. NOTE: I am not using the date fields provided with the date uri, just the date_popup form element.

You can override the default date_popup validation. The data_popup module applies the validation function during the date_popup_element_process function. 

I used a hook_element_info_alter function to append a custom process function AFTER the date_popup_element_process and applied my own validation function. Like so:

function hook_element_info_alter(&amp;$type) {
    $type['date_popup']['#process'][] = 'my_popup_date_process';
}

function my_popup_date_process($element, &amp;$form_state, $form) {
    $element['#element_validate'] = array('my_popup_date_validate');
    return $element;
}

function my_popup_date_validate() {
    if (isset($form_state['values'][$element['#field_name']])) {
        if (trim($form_state['values'][$element['#field_name']][$element['#language']][0]['time']) == '') {
            list($date_format, $time_format) = explode(" ", $element['#date_format']);
            $element['#date_format'] = trim($date_format);
        }
    }
    date_popup_validate($element, $form_state);
}


Removed unneeded code for brevity. Updated validation funciton with an example showing how this could be achieved. This example assumes that there is a space between the data and time formats (ie "d/m/Y H:i:s") and that the date format is first.