woocomerce-update_order_date_on_status_change.php

<?php

add_action('woocommerce_order_status_changed', 'mk_woocommerce_order_status_changed', 10, 4);

function mk_woocommerce_order_status_changed($order_id, $status_from, $status_to, $woo) {
    mk_woocommerce_update_order_date($order_id);
}

function mk_woocommerce_update_order_date($order_id, $post_status) {
    $oOrder = new WC_Order($order_id);

    $order_data = $oOrder->get_data();
    if (is_array($order_data)) {
        if (isset($order_data['id'])) {
            if ($order_data['id'] > 0) {
                $time = current_time('mysql');

                $args = array(
                    'post_id' => $order_data['id'],
                    'post_date' => $time,
                    'post_date_gmt' => get_gmt_from_date($time)
                );

                wp_update_post($args);
            }
        }
    }
}