Warning: date_timezone_set() expects parameter 1 to be DateTime, boolean given in format_date() (line 1909

Not sure if this is related to the module? Maybe check your node/fields/entity for breaking the date function somehow.

Ok, try the following. I added the date query type in search_api_ranges_facetapi_widgets().

/**
 * Implements hook_facetapi_widgets().
 */
function search_api_ranges_facetapi_widgets() {
  return array(
    'search_api_ranges_ui_slider' => array(
      'handler' => array(
        'label' => t('Ranges: Min/Max UI Slider'),
        'class' => 'SearchApiRangesWidgetUISlider',
        'query types' => array(
          'term',
          'date',
        ),
      ),
    ),
  );
}

Let me know if this has any influence?

So it's related to the format_date() function. Can you see where you call this function?

>> Besides sorting by date is displayed as a Unix time
Yes it is, it has to sort by the unix value. The module is not a perfect date slider, it can only slide numerical values like a Unix timestamp.

This module does not (yet) support date sliders, only integers/floats/decimals. Postponing until then.

I have no plans for dates, but if anyone supplies a patch, I will commit it.

My thoughts on the subject:

- the jQuery UI sliders can only slide integers (e.g. unix timestamps will work)
- implement date-pickers instead of regular input boxes?
- date slider could be extended in plugins/facetapi/widget_links.inc
- use some kind of preprocessing to represent timestamps as date_format (widget configuration option?)

Dates are supported, as long as you index dates as Unix timestamps. Then using the custom tpl.php file to theme your slider, change the text inputs to date-pickers that return a Unix timstamp.