Android : Add SeekBar value to initial value AndroidHere i

I have a initial Time value of 10:30. I also have two SeekBar one for number of hours and other for number of minutes.

When I slide the SeekBar to a certain value, for example for the Hour SeekBar, the number of hours get added to the initial time of 10:30. This works fine.

Further if I again drag the SeekBar to a new value, that value should be added to the initial value and not the value I obtain after the first drag.

ie. If at first I drag the SeekBar to 1 hour and leave the SeekBar, the time is 11.30.

If again I drag the value to 3 hours, the 3 hours get added to 11.30 making the time 2:30 whereas I want the time to be 1:30

Here is my code:-

String initialTime = "10:30"
cal = Calendar.getInstance();


        DateFormat sdf = new SimpleDateFormat("hh:mm:ss");
        Date date;
        try 
        {
            date = sdf.parse(initialTime);
            cal= Calendar.getInstance();
            cal.setTime(date);

            txtReachingBy.setText("Reaching By:"+" "+ cal.get(Calendar.HOUR_OF_DAY)+":"+cal.get(Calendar.MINUTE));
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
seekLateBy.setOnSeekBarChangeListener(new OnSeekBarChangeListener() 
        {


            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser)
            {
                progressChangedHours = progress;
                if(progressChangedHours==0 && progressChangedMins!=0)
                {
                    lblLateBy.setText("Late By (Hrs):"+" " + String.valueOf(progressChangedHours) +":"+String.valueOf(progressChangedMins));
                }
                else
                lblLateBy.setText("Late By (Hrs):"+" " + String.valueOf(progressChangedHours) +":"+String.valueOf(progressChangedMins));

            }



            public void onStartTrackingTouch(SeekBar seekBar) {
                // TODO Auto-generated method stub
            }

            public void onStopTrackingTouch(SeekBar seekBar) 
            {
                if(progressChangedHours==0)
                {
                    timeString = cal.get(Calendar.HOUR_OF_DAY)+":"+cal.get(Calendar.MINUTE)+":"+today.second;
                }
                else
                {
                cal.add(Calendar.HOUR_OF_DAY, progressChangedHours);

                timeString = cal.get(Calendar.HOUR_OF_DAY)+":"+cal.get(Calendar.MINUTE)+":"+today.second;
                }
                txtReachingBy.setText("Reaching by:"+" "+timeString);
            }





        }); 

How can I do this/