The first TX was sent on the: 2018-01-24 22:12:21, with a TX from @theymos to @AdolfinWolf, so that I guess is the official start (UTC). Ofcourse, it depends on your local time zone to determine if it started on the 24th or the 25th. @theymos's thread explaining the system was posted on the 25th (again depending on how one is set in relation to UTC), and that is when most people got to know it was in motion.