Time operations do not consider daylight savings

NOW()+INTERVAL 1800 SECOND produces invalid date.
Having a table with a column
`valid` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP

and an insert statement like this
REPLACE INTO tblCaptcha SET `valid`=NOW()+INTERVAL 1800 SECOND

produces the following error at 2021-03-28, 01:30:08
Incorrect datetime value: '2021-03-28 02:00:08' for column `tblCaptcha`.`valid` at row 1