WPFacet date formating

gistfile1.php

<?php

function my_facetwp_index_row( $params, $class ) {
    if ( 'keydate' == $params['facet_name'] ) { // 20170823
        $val = $params['facet_value'];
        $fixed = substr( $val, 0, 4 ) . '-' . substr( $val, 4, 2 ) . '-' . substr( $val, 6, 2 );
        $params['facet_value'] = $fixed;
        $params['facet_display_value'] = $fixed;
    }
    return $params;
}
add_filter( 'facetwp_index_row', 'my_facetwp_index_row', 10, 2 );