using System;

​

public class Program

{

    public static void Main()

    {

        DateTime date1 = new DateTime(2024, 1, 1, 8, 0, 15);

        DateTime date2 = new DateTime(2024, 8, 18, 13, 30, 20);

        TimeSpan timeSpan = date2 - date1;

        Console.WriteLine("Original Format: "+timeSpan.ToString());

        Console.WriteLine("New Format: "+timeSpan.BasedOnHours());

    }

}

​

public static class TimespanExtension

{

    public static string BasedOnHours(this TimeSpan timespan)

    {

        return $"{timespan.TotalHours:00}:{timespan.Minutes:00}:{timespan.Seconds:00}";

    }

}