IIRC, it was within hours of the first attack at the WTC when some of the names of the hijackers started to emerge.
Probably, the live thread during that day might show the timeframe. [I don't have a link to that live thread and have no idea how to search back to find it.]
Thanks, TomGuy. Someone will find a newspaper article printed on 9/12 which mentions Atta and others, I'll bet.