code: public void plusHours(long delta)
      {
          if (delta != 0)
          {
              long result = getHour() + delta;
              setHour((int) Math.floorMod(result, 24));
              plusDays(Math.floorDiv(result, 24));
          }
      }
docs: Adds delta hours. Delta can be negative. Month, year, day and hour fields
  are affected.
  @param delta