Customize date drill down level

I'd like to allow my site users to drill down to the month level only. I found the place where this is set to minute by default, in ApacheSolrFacetapiDate::getDateRange() in plugins/facetapi/query_type_date.inc. So I understand if I don't want to hack apachesolr I need to somehow override this method. Looking through the code, it seems the right way to do this is to implement my own query type plugin. I can implement something like this

/**
 * Implements hook_facetapi_query_types().
 */
function apachesolr_facetapi_query_types() {
  return array(
    'mysearch_date' => array(
      'handler' => array(
        'class' => 'MySearchFacetapiDate',
        'adapter' => 'apachesolr',
      ),
    ),
  );
}

and include my MySearchFacetapiDate class via my .info.

What I don't understand though is how my custom query type 'mysearch_date' is going to be used instead of the default apachesolr_date. I've grepped 'apachesolr_date' (key used in the apachesolr hook implementation) through apachesolr but I failed to see where this is set so that Drupal/FacetApi knows to use my custom query type. Also checked my export facet settings and could not find it.