MySQL 8.0

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select version();

version()

8.0.36

CREATE TABLE ForgeRock
	(`id` int, `dateTime` datetime)
;
INSERT INTO ForgeRock
	(`id`, `dateTime`)
VALUES
	(1, '2015-08-04 13:40:56')
;
SELECT 
  TO_SECONDS(f.`dateTime`) AS `to_seconds`, 
  f.`dateTime` AS `actual`
FROM ForgeRock AS f;

to_seconds
actual

63605914856
2015-08-04 13:40:56

SET @@session.time_zone = "-04:00";

SELECT 
  '0000-01-01' + INTERVAL TO_SECONDS(f.`dateTime`) SECOND - INTERVAL 1 DAY AS `from_seconds`, 
  f.`dateTime` AS `actual`
FROM ForgeRock AS f;

from_seconds
actual

2015-08-04 13:40:56
2015-08-04 13:40:56

SET @@session.time_zone = "-04:00";

SELECT 
  FROM_UNIXTIME(TO_SECONDS(f.`dateTime`) - TO_SECONDS('1970-01-01 00:00:00')) AS `incorrect_unix`,
  f.`dateTime`  AS `actual`
FROM ForgeRock AS f;

incorrect_unix
actual

2015-08-04 09:40:56
2015-08-04 13:40:56

SET @@session.time_zone = "-04:00";

SELECT TIMESTAMPDIFF(MINUTE, UTC_TIMESTAMP(), NOW()) AS `utc_tz_offset`;

SELECT 
  FROM_UNIXTIME(TO_SECONDS(f.`dateTime`) - TO_SECONDS('1970-01-01 00:00:00')) - INTERVAL TIMESTAMPDIFF(MINUTE, UTC_TIMESTAMP(), NOW()) MINUTE AS `unix_utc_tz`,
  f.`dateTime`  AS `actual`
FROM ForgeRock AS f;

utc_tz_offset

-240

unix_utc_tz
actual

2015-08-04 13:40:56
2015-08-04 13:40:56