code: public void setGapSize(int gapSize, ConstantSize.Unit units) {
          ConstantSize gapSizeObject = new ConstantSize(gapSize, units);
          ColumnSpec columnSpec = ColumnSpec.createGap(gapSizeObject);
          FormLayout layout = (FormLayout) getLayout();
          layout.setColumnSpec(2, columnSpec);
      }
docs: setGapSize, This sets the size of the gap between the date picker and the time picker.