using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        int horaInicial = 8;

        int horaFinal = 18;

​

        DateTime date = new DateTime(2022,09,26,23,00,00);

        if ((date.DayOfWeek != DayOfWeek.Saturday && date.DayOfWeek != DayOfWeek.Sunday/* Domingo */))//&& !IsHoliday(date.Day, date.Month, date.Year))

        {

            DateTime lastUpdate = date.AddHours(-8);

            Console.WriteLine(lastUpdate);

            if(date.DayOfWeek == DayOfWeek.Monday && (lastUpdate.Hour < 8 || lastUpdate.Hour > 18)){

                date = date.AddHours(-72);

                lastUpdate = new DateTime(date.Year, date.Month, date.Day, 18,00,00);

            }

            if(lastUpdate.Hour < 8){

                int remainHour = 8 - lastUpdate.Hour;

                lastUpdate = lastUpdate.AddHours(remainHour * -1);

            }else if(lastUpdate.Hour >= 18){

                lastUpdate = lastUpdate.AddHours(-8);

            }

            List<DateTime> allHolidays = GetHoliday(lastUpdate.Day, lastUpdate.Month, lastUpdate.Year);

            foreach(DateTime dateHoliday in allHolidays.OrderByDescending(h => h.Day)){

                if(dateHoliday.Day == lastUpdate.Day){

                    lastUpdate = lastUpdate.AddHours(-24);

                }

            }

            Console.WriteLine(lastUpdate);

        }

    }

    public static List<DateTime> GetHoliday(int day, int month, int year){

        return new List<DateTime>() {

            new DateTime(2022, 09, 23),

            new DateTime(2022, 09, 21),

            new DateTime(2022, 09, 20),

        };

    }

}