using System;

using System.Collections.Generic;

public class Program

{

        public static void Main()

        {

            string FormatDateTime = "yyyy-MM-dd HH:mm:ss.fff";

            List<string> newList = new List<string>();

            newList.Add("2021-07-12 07:23:32.770");

            newList.Add("2021-07-12 07:22:30.060");

            newList.Add("2021-07-12 07:25:32.790");

            newList.Add("2021-07-12 07:23:30.040");

            newList.Add("2021-07-12 07:24:32.810");

            newList.Add("2021-07-12 07:21:30.080");

            newList.Add("2021-07-12 07:25:32.820");

            newList.Add("2021-07-12 07:23:30.010");

            newList.Add("2021-07-12 07:24:32.840");

            newList.Add("2021-07-12 07:21:29.990");

            newList.Add("2021-07-12 07:24:32.750");

            newList.Add("2021-07-12 07:23:29.980");

            newList.Add("2021-07-12 07:24:32.870");

​

            List<long> listFormatDate = new List<long>();

            List<long> result = new List<long>();

            List<long> listResult = new List<long>();

​

            for (int i = 0 ; i < newList.Count; i++)

            {

                DateTime myDate = DateTime.ParseExact(newList[i], FormatDateTime, System.Globalization.CultureInfo.InvariantCulture);

                listFormatDate.Add(myDate.Ticks / 10000);

            }

​

            for (int i = 0; i < listFormatDate.Count; i++)

            {

                result.Add(listFormatDate[i]);

            }

            int number = 0;

            while (number < listFormatDate.Count)

            {

                long tong = 0;

                result.Clear();

                for (int i = 0; i < listFormatDate.Count; i++)

                {

                    if (number != i)

                    {

                        result.Add(listFormatDate[i]);

                    }

                }

                result.Sort();

                result.RemoveAt(0);

                result.RemoveAt(result.Count - 1);

                for (int i = 0; i < result.Count; i++)

                {

                    tong += result[i];

                }

                double x = tong / result.Count;

                listResult.Add((long)Math.Round(x, 0, MidpointRounding.AwayFromZero));

                number++;

            }

            for (int i = 0; i < listResult.Count; i++)

            {

                DateTime myDate = new DateTime(listResult[i]*10000);

                String kq = myDate.ToString(FormatDateTime);

                Console.WriteLine(kq);

            }

        }

}

​