FacetWP - modify date_range facet to find posts on a certain day

test.php

<?php

function fwp_match_exact_day( $return, $params ) {
    $facet = $params['facet'];
    $values = $params['selected_values'];

    if ( 'YOUR_FACET_NAME' == $facet['name'] ) {
        global $wpdb;

        $where = '';
        if ( '' != $values[0] ) {
            $where .= " AND LEFT(facet_value, 10) = '{$values[0]}'";
        }

        $sql = "
        SELECT DISTINCT post_id FROM {$wpdb->prefix}facetwp_index
        WHERE facet_name = '{$facet['name']}' $where";
        return $wpdb->get_col( $sql );
    }
    return $return;
}
add_filter( 'facetwp_facet_filter_posts', 'fwp_match_exact_day', 10, 2 );

Hi, I'm interested in this gist but I'm not sure to fully understand how it works…
I'm trying to filter posts which custom date field is older than today, don't know if I can customize this code to achieve that :)