using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        int tminusDay = 30, window = 1;

        DateTime startDateOfRenewal = new DateTime(2018, 9, 1);

        DateTime endDateOfRenewal = new DateTime(2018, 10, 1).AddDays(-1);

        DateTime test = Convert.ToDateTime("9/4/2018 1:30:35 AM"); //DateTime.Today;

        if (true &&

                endDateOfRenewal.AddDays(-tminusDay) <= test &&

                test <= endDateOfRenewal.AddDays(-tminusDay + window))

            {

            Console.WriteLine("Here");

        }

    }

}