MIT is hosting the first, last, and only Time Traveler Convention on May 7th, 2005 in the East Campus Courtyard. As their announcement points out:
Technically, you would only need one time traveler convention. Time travelers from all eras could meet at a specific place at a specific time, and they could make as many repeat visits as they wanted.
So to help out, scratch out these temporal-spacial coordinates on a hunk of metal and throw it into your local salt mine:
Time Traveler’s Convention! May 7, 2005, 1 hour 56 minutes past sunset, 42:21:36.025°N, 71:05:16.332°W
(Thanks to Josh for the link!)
Update 9/22/5566: The conference was a blast! If you wind up going (and I recommend you do) be sure to say hello — I’ll be the one with the green sports blazer, red fez and blue tentacles.