code: public function setTimezone( $timezone ) {
  		try {
  			$this->timestamp->setTimezone( new DateTimeZone( $timezone ) );
  		} catch ( Exception $e ) {
  			throw new TimestampException( __METHOD__ . ': Invalid timezone.', $e->getCode(), $e );
  		}
  	}
docs: Set the timezone of this timestamp to the specified timezone.
  
  @param string $timezone Timezone to set
  @throws TimestampException