using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

         var dateNow =new DateTime(2021,10,05,08,15,00);

         int FromYear = 2021;

         int FromMonth = 08;

         int ToYear = 2021;

         int ToMonth = 08;

            var daysInMonth = DateTime.DaysInMonth(ToYear, ToMonth);

            Console.WriteLine (@"daysInMonth"+daysInMonth);

            var fromDate = new DateTime(FromYear,FromMonth, 1);

            var toDate = new DateTime(ToYear, ToMonth, daysInMonth);

​

            if (dateNow.Date == fromDate.Date)

            {

                fromDate = fromDate.AddMonths(-1);

                toDate = toDate.AddDays(-1).AddMonths(-1);

                Console.WriteLine (@"dateNow.Date == fromDate.Date");

                Console.WriteLine (@"dateNow:"+dateNow.ToString("dd/MM/yyyy HH:mm:ss"));

                Console.WriteLine (@"fromDate:"+fromDate.ToString("dd/MM/yyyy HH:mm:ss"));

                Console.WriteLine (@"toDate:"+toDate.ToString("dd/MM/yyyy HH:mm:ss"));

                 TimeSpan avaiableCutOfTime;

            if (!TimeSpan.TryParse("09:00", out avaiableCutOfTime))

            {

               Console.WriteLine (@"TimeSpan.TryParse avaiableCutOfTime");

               Console.WriteLine ("Throw Error");

            }

                if (dateNow.TimeOfDay < avaiableCutOfTime)

            {

                toDate = toDate.AddDays(-1);

                Console.WriteLine (@"dateNow.TimeOfDay < avaiableCutOfTime.TimeOfDay");

                Console.WriteLine (@"dateNow:"+dateNow.ToString("dd/MM/yyyy HH:mm:ss"));

                Console.WriteLine (@"fromDate:"+fromDate.ToString("dd/MM/yyyy HH:mm:ss"));

                Console.WriteLine (@"toDate:"+toDate.ToString("dd/MM/yyyy HH:mm:ss"));

            }

            }

            else if (dateNow.Month == ToMonth && dateNow.Year == ToYear)

            {

                toDate = dateNow.AddDays(-1);

                Console.WriteLine (@"dateNow.Month == ToMonth && dateNow.Year == ToYear");

                Console.WriteLine (@"dateNow:"+dateNow.ToString("dd/MM/yyyy HH:mm:ss"));

                Console.WriteLine (@"fromDate:"+fromDate.ToString("dd/MM/yyyy HH:mm:ss"));

                Console.WriteLine (@"toDate:"+toDate.ToString("dd/MM/yyyy HH:mm:ss"));

            }

            if (fromDate > toDate)

            {

               Console.WriteLine (@"fromDate > toDate");

               Console.WriteLine ("Throw Error");

            }

​

                Console.WriteLine (@"dateNow:"+dateNow.ToString("dd/MM/yyyy HH:mm:ss"));

                Console.WriteLine (@"fromDate:"+fromDate.ToString("dd/MM/yyyy HH:mm:ss"));

                Console.WriteLine (@"toDate:"+toDate.ToString("dd/MM/yyyy HH:mm:ss"));

​

    }

}