Query: How soon after planes crashed into them did the WTC towers collapse?
Context: The hijackers – members of al-Qaeda's Hamburg cell – intentionally crashed two airliners into the Twin Towers of the World Trade Center in New York City. Both buildings collapsed within two hours from fire damage related to the crashes, destroying nearby buildings and damaging others. The hijackers crashed a third airliner into the Pentagon in Arlington County, Virginia, just outside Washington D.C.