Auto lock forum posts with cron job?

I am using a forum software called esoTalk ([login to view URL]) as an artist critique forum where people upload work to be critiqued every week (every Sunday night) and members are given until the following Saturday night to critique each others work. The cycle starts all over again the following Sunday night. What I'd like to do is have an automatic auto lock feature where all posts that were created > 6 days ago in a particular channel ("to be critiqued") gets locked and moved to another channel (e.g. "Archive"). In this way, the critique channel will only show the new posts to be critiqued for the following week. This would be a scheduled feature that occurs say, Sunday morning at 3am EST. esotalk is a free, open-source forum software package built with PHP and MySQL I've been told what I want can be done with a cron job.