using System;

public class Program

{

    public static void Main()

    {

        var caseOpenedOn = new DateTime(7,1,1,5,6,0);

        var fir = new DateTime(7,1,1,5,5,0);

​

        var openCycleTimeInDays = Math.Abs((fir - caseOpenedOn).TotalDays);

        Console.WriteLine($"openCycleTimeInDays: {openCycleTimeInDays}");

    }

}