The ??? itself stays for random time periods, or until examined for the quest. It has been seen to stay in the same place anywhere from 5 minutes to 3 hours. As of July 2008, two of us did this quest at the same time. We split up to search for the "???". It actually targets as a "Jar" and did not move after 10 seconds. In fact, I got mine at a location, and by chance the "Jar" repopped there a minute later, and my partner had the time to run across the map to get his from the same location. I dont know the repop chances or order, but I do know that it targets as "Jar" and did NOT move after 10 seconds.