code: public final void setTimeZone(final TimeZone timezone) {
          getStart().setUtc(false);
          getStart().setTimeZone(timezone);
          getEnd().setUtc(false);
          getEnd().setTimeZone(timezone);
      }
docs: Updates the start and (possible) end times of this period to reflect
  the specified timezone status.
  @param timezone a timezone for the period