private void refreshDurationField() {
		final Color defaultColor = Color.BLACK;
		final Color errorColor = Color.RED;
				
		if (startTimeDateChooser.getCalendar() == null) {
			startTimeDateChooser.setCalendar(Calendar.getInstance());
		}
		if (endTimeDateChooser.getCalendar() == null) {
			endTimeDateChooser.setCalendar(Calendar.getInstance());
		}
		long duration = Controller.calculateDuration(getStartTimeFromFields(), getEndTimeFromFields());
		txtDuration.setForeground((duration >= 0) ? defaultColor : errorColor);
		String durationString = Controller.getDurationString(duration);
		txtDuration.setText(durationString);
	}