Deve se passar a data para dar certo o cálculo
Forma
DateTime dateIni = DateTime.ParseExact("21/01/2001 07:30", "dd/MM/yyyy HH:mm", null);
DateTime dateEnd = DateTime.ParseExact("22/01/2001 16:40", "dd/MM/yyyy HH:mm", null);
TimeSpan dater = dateEnd.Subtract(dateIni);
System.Console.WriteLine("{0:00}:{1:00}", (dater.Days * 24) + dater.Hours, dater.Minutes);
System.Console.ReadKey();
Fulvio Cezar Canducci Dias

