As Floffe said, it was in the afternoon our time. I don't entirely remember if I saw it on TV still in school, or only a bit later when I got back home. Definitely remember discussing it that night on wotmania, though.
The other big one over here were the terrorist attack on Brussels Airport and the subway, a couple of years ago, was in the office for that one. Of course nothing like 9/11 in terms of numbers or traumatizing live footage, nor can I say it left the same impact (couldn't even tell you off the top of my head what the date was...), but Belgium is a pretty small country and tons of people knew someone who, if not actually affected by the attacks themselves, had passed through that subway station or the airport that day and easily could have been.