This is more ridiculous BS by Homeland Security giving half-assed explanations.
A week ago, an Al Qaeda operation was picked up in Pakistan (or nearby). One of the terrorists appears to be a guy involved in some embassy bombing. Bush adminstration anounce the capture on Thursday (day of Kerry's speech).
According to news, there were some laptops recovered. The laptops had detailed surveilance information about the targets announced today.
Based on the detailed level of surveilance, the alert was issued. THEY HAVE ABSOLUTELY NO IDEA WHEN A STRIKE IS PLANNED. (or if they do, they are withholding this from the public) This could be months or more away. Anybody not showing up for work tomorrow is overreacting.