It’s hard to tell because old threads aren’t really time stamped, but it looks like this thread on 9/11 was started just after the first plane hit. Near the end the thread there’s a post about an announcement at 3:15 Pacific time, or 6:15 Eastern time. The mods then closed the thread at 400 posts, which would mean the last post was probably about 9 1/2 hours after the first - an average of more than 40 posts per hour.