/// <summary>
        /// 獲取網路日期時間
        /// </summary>
        /// <returns></returns>
        public static string GetNetDateTime()
        {
            WebRequest request = null;
            WebResponse response = null;
            WebHeaderCollection headerCollection = null;
            string datetime = string.Empty;
            try
            {
                request = WebRequest.Create("https://www.baidu.com");
                request.Timeout = 3000;
                request.Credentials = CredentialCache.DefaultCredentials;
                response = (WebResponse)request.GetResponse();
                headerCollection = response.Headers;
                foreach (var h in headerCollection.AllKeys)
                { if (h == "Date") { datetime = headerCollection[h]; } }
                return datetime;
            }
            catch (Exception) { return datetime; }
            finally
            {
                if (request != null)
                { request.Abort(); }
                if (response != null)
                { response.Close(); }
                if (headerCollection != null)
                { headerCollection.Clear(); }
            }
        }

【2】呼叫

            string dt = GetNetDateTime();
            Console.WriteLine(Convert.ToDateTime(dt).ToString("yyyy-MM-dd HH:mm:ss"));
            Console.ReadLine();

            2017-04-16 21:04:21