protected function format_date( $date, $type ) {

		switch ( $type ) {

			case 'start':
				$date .= ' 00:00:00';

				break;

			case 'end':
				/**
				 * Return 00:00:00 on the next day after this date, using PHP datetime functions to avoid issues with daylight savings time or leap years.
				 *
				 * 23:59:59 is not a safe way to capture the end of day in newer versions of MySQL, if the transaction happened at (say) 23:59:59.999.
				 */
				$end_date = new DateTime( $date );
				$end_date->modify( '+1 day' );

				$date = $end_date->format( 'Y-m-d' ) . ' 00:00:00';

				break;

		}

		return $date;
	}