Below I have a List of Time to be added together

  List<String> arrTime = new ArrayList<String>();
  int hour      = 0;
  int minutes   = 0;
  int seconds   = 0;
  String Nmin   = null;
  String Nsec   = null;
  String result = null;

  arrTime.add("09:05:25");
  arrTime.add("09:30:15");
  arrTime.add("10:15:01");
  arrTime.add("08:19:49");
  arrTime.add("09:17:40");

  for (Iterator itr = arrTime.iterator(); itr.hasNext();) 
  {
    String Time = (String) itr.next();

    if (Time != null) 
    {
      String[] rowtime = Time.split(":");
      hour            += Integer.parseInt(rowtime[0]);
      minutes         += Integer.parseInt(rowtime[1]);
      seconds         += Integer.parseInt(rowtime[2]);
    }
  }

  hour    += minutes/60;
  minutes += seconds/60;

  minutes %= 60;
  seconds %= 60;

  if (minutes < 10)
   Nmin = "0" + String.valueOf(minutes);
  else
   Nmin = String.valueOf(minutes);
	 
  if (seconds < 10)
   Nsec = "0" + String.valueOf(seconds);
  else
   Nsec = String.valueOf(seconds);

  result = hour + ":" + Nmin + ":" + Nsec;
  
  System.out.println(result);

Output
46:28:10