code: private void tryStartingKbMode(int keyCode) {
          if (mTimePicker.trySettingInputEnabled(false) &&
                  (keyCode == -1 || addKeyIfLegal(keyCode))) {
              mInKbMode = true;
              mDoneButton.setEnabled(false);
              updateDisplay(false);
          }
      }
docs: Try to start keyboard mode with the specified key, as long as the timepicker is not in the
  middle of a touch-event.
  
  @param keyCode The key to use as the first press. Keyboard mode will not be started if the
  key is not legal to start with. Or, pass in -1 to get into keyboard mode without a starting
  key.