If it is cron and php, they don't really need Opencart as such. Just according to schedule runs the php script Kron, he climbs into the database and changes kaki some data. All. And this whole scheme is absolutely not important it's Opencart or something else. The script only needs to know that there is a base (its name), you need a password and user to access it, the table, in it the row number and column name in which it is necessary to change the digit.