Returns the number of seconds between two dates with times. You can indicate if you want to include only working days. If you add the table, holidays are excluded

holliday_table.sql

CREATE TABLE `holliday_table` (
  `_date` date NOT NULL DEFAULT '0000-00-00',
  `_desc` varchar(60) NOT NULL DEFAULT '' COMMENT 'Description',
  PRIMARY KEY (`_date`),
  KEY `_desc` (`_desc`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='Holliday table';

SECONDS_BETWEEN_TIMESTAMP.sql

DROP FUNCTION IF EXISTS SECONDS_BETWEEN_TIMESTAMP;
DELIMITER $$
CREATE FUNCTION `SECONDS_BETWEEN_TIMESTAMP`(START_TIMESTAMP TIMESTAMP, END_TIMESTAMP TIMESTAMP, RETURN_RESULT VARCHAR (20)) RETURNS BIGINT(20) CHARSET utf8
    READS SQL DATA
    DETERMINISTIC
BEGIN
  DECLARE TOTAL_SECS INTEGER;
  DECLARE START_DATE DATE;
	DECLARE END_DATE DATE;
	DECLARE TOTAL_DAY_SAT INTEGER;
	DECLARE TOTAL_DAY_SUN INTEGER;
	DECLARE TOTAL_DAY_WEND INTEGER;
	DECLARE TOTAL_HOLLIDAY INTEGER;
  DECLARE RESULT INTEGER;
  DECLARE CURR_DATE DATE;
  IF (TIMESTAMPDIFF(SECOND, START_TIMESTAMP, END_TIMESTAMP) < 0) THEN RETURN -1; END IF;

  SET TOTAL_SECS = TIMESTAMPDIFF(SECOND, START_TIMESTAMP, END_TIMESTAMP);
  IF (RETURN_RESULT = "SECS_TOTAL") THEN RETURN TOTAL_SECS; END IF;

  SET START_DATE = CAST(START_TIMESTAMP AS DATE);
  SET END_DATE = CAST(END_TIMESTAMP AS DATE);
	IF (DATEDIFF(END_DATE, START_DATE) > 7) THEN
    SET TOTAL_DAY_SAT = (FLOOR(DATEDIFF(END_DATE, START_DATE) / 6) * 86400);
    SET TOTAL_DAY_SUN = (FLOOR(DATEDIFF(END_DATE, START_DATE) / 7) * 86400);
	ELSE
	  SET CURR_DATE = START_DATE;
    SET TOTAL_DAY_SAT = 0;
    SET TOTAL_DAY_SUN = 0;
    loop_label: LOOP
		  IF (DAYNAME(CURR_DATE) = "Saturday") THEN
			  SET TOTAL_DAY_SAT = TOTAL_DAY_SAT + 1;
			END IF;
		  IF (DAYNAME(CURR_DATE) = "Sunday") THEN
			  SET TOTAL_DAY_SUN = TOTAL_DAY_SUN + 1;
			END IF;
			SET CURR_DATE = DATE_ADD(CURR_DATE, INTERVAL 1 DAY);
		  IF CURR_DATE > END_DATE THEN
			  SET TOTAL_DAY_SAT = TOTAL_DAY_SAT * 86400;
			  SET TOTAL_DAY_SUN = TOTAL_DAY_SUN * 86400;
			  LEAVE loop_label;
		  END IF;
      ITERATE loop_label;
    END LOOP;
	END IF;
	SET TOTAL_DAY_WEND = TOTAL_DAY_SAT + TOTAL_DAY_SUN;
	IF (RETURN_RESULT = "SECS_WO_WENDS") THEN RETURN (TOTAL_SECS - TOTAL_DAY_WEND); END IF;
	IF (RETURN_RESULT = "SECS_WO_SAT") THEN RETURN (TOTAL_SECS - TOTAL_DAY_SAT); END IF;
  IF (RETURN_RESULT = "SECS_WO_SUN") THEN RETURN (TOTAL_SECS - TOTAL_DAY_SUN); END IF;
	SET TOTAL_HOLLIDAY = IFNULL((SELECT SUM(IF(holliday_table._date BETWEEN START_DATE AND END_DATE, 1, 0)) AS numofdays FROM holliday_table), 0) * 86400;
  IF (RETURN_RESULT = "SECS_WO_HOLLIDAYS") THEN RETURN (TOTAL_SECS - TOTAL_HOLLIDAY); END IF;
	IF (RETURN_RESULT = "SECS_ONLY_WORKDAYS") THEN RETURN (TOTAL_SECS - (TOTAL_HOLLIDAY + TOTAL_DAY_WEND)); END IF;
	SET RESULT = 0;
RETURN RESULT;
END
$$
DELIMITER ;