I had that happen to me - it was the server that malfunctioned and the date jumped. I had to change the date back and then edit all the times manually (threads, posts, PMs, etc.) It jumped nearly within a few minutes of 8 hours less than 1 year ahead. I rounded it to 8 hours off of 1 year. Figuring out everything based on unixtime was a blast...

I spent several hours fixing this.