MySQL DateTime vs. TimeStamp vs. TimeZone changes.

MySQL.sql

mysql> CREATE TABLE `timetest` (`datetime` DATETIME DEFAULT 0, `timestamp` TIMESTAMP DEFAULT 0);
Query OK, 0 rows affected (0,29 sec)

mysql> DESCRIBE `timetest`;
+-----------+-----------+------+-----+---------------------+-------+
| Field     | Type      | Null | Key | Default             | Extra |
+-----------+-----------+------+-----+---------------------+-------+
| datetime  | datetime  | YES  |     | 0000-00-00 00:00:00 |       |
| timestamp | timestamp | NO   |     | 0000-00-00 00:00:00 |       |
+-----------+-----------+------+-----+---------------------+-------+
2 rows in set (0,00 sec)

mysql> INSERT INTO `timetest` VALUES ('2018-03-13 00:00:00', '2018-03-13 00:00:00');
Query OK, 1 row affected (0,01 sec)

mysql> SELECT @@time_zone, `datetime`, UNIX_TIMESTAMP(`datetime`) `dt`, `timestamp`, UNIX_TIMESTAMP(`timestamp`) `ts` FROM `timetest`;
+-------------+---------------------+------------+---------------------+------------+
| @@time_zone | datetime            | dt         | timestamp           | ts         |
+-------------+---------------------+------------+---------------------+------------+
| SYSTEM      | 2018-03-13 00:00:00 | 1520888400 | 2018-03-13 00:00:00 | 1520888400 |
+-------------+---------------------+------------+---------------------+------------+
1 row in set (0,00 sec)

mysql> SET @@time_zone='Europe/Moscow';
Query OK, 0 rows affected (0,00 sec)

mysql> SELECT @@time_zone, `datetime`, UNIX_TIMESTAMP(`datetime`) `dt`, `timestamp`, UNIX_TIMESTAMP(`timestamp`) `ts` FROM `timetest`;
+---------------+---------------------+------------+---------------------+------------+
| @@time_zone   | datetime            | dt         | timestamp           | ts         |
+---------------+---------------------+------------+---------------------+------------+
| Europe/Moscow | 2018-03-13 00:00:00 | 1520888400 | 2018-03-13 00:00:00 | 1520888400 |
+---------------+---------------------+------------+---------------------+------------+
1 row in set (0,00 sec)

mysql> SET @@time_zone='America/Belize';
Query OK, 0 rows affected (0,00 sec)

mysql> SELECT @@time_zone, `datetime`, UNIX_TIMESTAMP(`datetime`) `dt`, `timestamp`, UNIX_TIMESTAMP(`timestamp`) `ts` FROM `timetest`;
+----------------+---------------------+------------+---------------------+------------+
| @@time_zone    | datetime            | dt         | timestamp           | ts         |
+----------------+---------------------+------------+---------------------+------------+
| America/Belize | 2018-03-13 00:00:00 | 1520920800 | 2018-03-12 15:00:00 | 1520888400 |
+----------------+---------------------+------------+---------------------+------------+
1 row in set (0,00 sec)

mysql>