How to create a temporary string in mysql?

Question

PHP

I am making an online store for the provision of goods with a time frame.
After a successful payment, a unique key for the user is generated based on the initial payment data (by amount), and this unique string is entered into the database. After that, the buyer activates this key with a POST request on the main page, and this key is compared in the database, that such a key (string) is in the database, after the buyer gets access to a certain temporary product.
The essence of the question is the following, how do I set the time frame for this unique string (key)?

Answer 1

Columns dt_startand dt_end, DateTime type?

SELECT code, dt_end
FROM tbl_codes
WHERE code = :code
    AND NOW() >= dt_start
    AND NOW() <= dt_end;