<?php
add_filter('wp_insert_post_data', 'wpp_wc_save_post', '9999', 2);

function wpp_wc_save_post($data, $postarr)
{

    if ($data['post_type'] == 'shop_order')
        $_POST['order_date'] = gregdate('Y-m-d', $_POST['order_date']);
    if ($data['post_type'] == 'product') {
        if (isset($_POST['_sale_price_dates_from']) and !empty($_POST['_sale_price_dates_from'])) {
            $_POST['_sale_price_dates_from'] = gregdate('Y-m-d', $_POST['_sale_price_dates_from']);
        }
        if (isset($_POST['_sale_price_dates_to']) and !empty($_POST['_sale_price_dates_to'])) {
            $_POST['_sale_price_dates_to'] = gregdate('Y-m-d', $_POST['_sale_price_dates_to']);
        }
    }
    return $data;
}

function getqtlangcustomfieldvalue($metadata, $object_id, $meta_key, $single)
{

    if ($meta_key == '_sale_price_dates_from') {
        var_dump($_POST);
        var_dump(func_get_args());//die;
    }
    if ($meta_key == '_sale_price_dates_to') {
        var_dump($_POST);
        var_dump(func_get_args());//die;
    }

}

add_filter('update_post_metadata', 'getqtlangcustomfieldvalue', 10, 4);