Post Expire based on Custom Field

I may be missing something here but I have a custom field expiration-date in which I set to a UNIX timestamp and in the past the plugin has automatically expired the post based on this date.

This is not working and therefore I have posts which are outdated because I cannot get them to expire unless I perform manually but this is unfeasible.

Any help appreciated.

http://wordpress.org/plugins/post-expirator/