I have long suspected the Pizzanigger of manually editing the database to change the facts without anyone being able to tell, ie. editing posts without adding the Last Edited message at the bottom. Changing timestamps is the same exact process. There's not really anything stopping him from doing this.
This is the kind of side effects I'd expect to see if the post timestamps were moved into the future.
I wouldn't be a bit surprised if his fucking around eventually triggers a bug in XenForo resulting in an unrecoverable error.