In dagon's post above, the 'NOW' should have been a function call; see NOW() in the MySQL manual.
In addition, note that the INTERVAL keyword expects the unit name to be singular, so you'd use 'MINUTE' rather than 'MINUTES' (yes, saying something like '30 MINUTE' sounds horribly wrong, but alas that's what MySQL expects). See the MySQL manual page for DATE_ADD() for more info, as it explains how to use the INTERVAL keyword.