First off... really? I feel like you guys implemented this feature after one person complained about getting a troll review and jumped right into it. You should step back before you treat your site's users like children.
But also, it doesn't work properly. If I download the mod and go back, I could still be locked out from leaving a rating more than 15 minutes later, as it doesn't check at the moment the AJAX pops up.
If it were my site, I wouldn't do this at all, but since it is your site, can you at least fix it to work as intended.