SQL trigger to check for time interval

Hi,

I'm developing an application to manage/register users. Users can check in in our venue, but only once every 12 hours to prevent abuse.

I have a table that looks like this:

Code:

CREATE TABLE check_ins (
user BIGINT UNSIGNED,
time DATETIME NOT NULL DEFAULT NOW(),
CONSTRAINT check_ins_user_check_intime_uq UNIQUE (user, time),
CONSTRAINT check_ins_user_fk FOREIGN KEY (user) REFERENCES users(user_id) ON DELETE CASCADE
);

To do the 12h check I'm currently getting the current time from the server, and the time of the user's last checkin, then I compare it and insert it if valid.

Now I'd like to make it a little "cleaner" and just insert the user_id and NOW() into the table.
Then there be should trigger to check right before the insert if the time is allowed.
Something like NOW() - INTERVAL 12 HOURS > (SELECT MAX(time) FROM check_ins WHERE user = userToInsert)

Then if the check fails the sql execution throws an exception which I catch in my code.

Is this possible?

Thanks,
Stan