Ach, I was going to do something really scientific and study the daily, weekly and monthly variations and come up with a great guess .. but I'll just roll the dice go with Mon Sep 23 20:30:00 which will be right in the middle of my Monday night chorus rehearsal.
That last time I took part in a pool like this we (the regulars of the CANOPUS form on CompuServe) were guessing the release date of Windows 95. That was pretty funny. :)