code: public void setDayDateTimeFormatter(DateTimeFormatter formatter) {
          if (getFormatterMap().get(ViewType.DAY_VIEW) == null) {
              getFormatterMap().put(ViewType.DAY_VIEW, formatter);
          } else {
              getFormatterMap().replace(ViewType.DAY_VIEW, formatter);
          }
      }
docs: Sets the DateTimeFormatter on the Day Label located in the day page.
  Notice that this is also affecting the page that is going to be printed.
  
  @param formatter
  the DateTimeFormatter