I doubt it. I bet lots of people in either tower would have triggered the "I'm OK" feature a few minutes after the first plane hit, as would firemen who would only later get called in to help.

Should Facebook have created a 'please reconfirm' feature? If so, how often should hey have triggered it? For 9/11, there are at least four main events: two plane hits and two building collapses, but there were more: additional buildings, etc.