using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {   

        var fileYear = 2020;

        var fileMonth = 2;

        var startDate = new DateTime(2020, 9, 1);

        var endDate = new DateTime(2020, 9, 30);

        var daysInMonth = DateTime.DaysInMonth(fileYear, fileMonth);

​

        Console.WriteLine(daysInMonth);

        var hoursInMonth = daysInMonth * 24;

        Console.WriteLine(hoursInMonth);

​

        int startHour = 0;

​

        if (startDate.Year == fileYear &&

            startDate.Month == fileMonth &&

            startDate.Day != 1)

        {

            startHour = (startDate.Day - 1) * 24;

        }

​

        var timeIndices = Enumerable.Range(startHour, hoursInMonth - startHour);

​

        if (endDate.Year == fileYear &&

            endDate.Month == fileMonth &&

            endDate.Day != daysInMonth)

        {

            var endHour = endDate.Day * 24;

​

            timeIndices = timeIndices.Where(x => x < endHour);

        }

        Console.WriteLine(timeIndices.Count());

        Console.WriteLine(string.Join(", ", timeIndices));

    }

}