code: public void plusMinutes(long delta)
      {
          if (delta != 0)
          {
              long result = getMinute() + delta;
              setMinute((int) Math.floorMod(result, 60));
              plusHours(Math.floorDiv(result, 60));
          }
      }
docs: Adds delta minutes. Delta can be negative. Month, year, day, hour and
  minute fields are affected.
  @param delta