Denis,
You could work it into the query when authenticating - which would probably be the easiest method.
You would do this by comparing your column's time to CURTIME() or CURDATE(). Those are simple MySQL commands that can be used right in your query as is and will return either the exact Current Time or Current Date... so you simply add a clause to your recordset Select stament making it say WHERE mytime < CURTIME(). Then if no record is returned, you don't allow authentication and create a redirect.
Cheers,
Brian
