C＃时间跨度转换矩产生不同的结果

Question

TimeSpan dayDuration = new TimeSpan(23,59,59);
            var x =dayDuration.Subtract(new TimeSpan(23, 59, 59)).Subtract(Convert.ToDateTime("2019-02-01 18:00").TimeOfDay);


            Console.WriteLine(dayDuration);
            Console.WriteLine(x);
            Console.ReadLine();

此Timespan如何产生o / p：如-18：00：00 但是当我在js

 let dayDuration ="23:59:59";
dayDuration = moment(moment("HH:mm:ss").diff(moment("2019-02-01 18:00","HH:mm:ss"))).utc().format("HH:mm:ss");

哪个会产生o.p，如05:59:59：我现在需要C＃o / p