I think Bear is thinking of that, plus a lot more. Like Http connections are supposed to not wait that long. Plus doesn't the container only have one instance of the Servlet, and putting that to sleep would disallow others from making requests.
It sounds like you are more trying to send an asynchronous message, which would be better solved with Message Driven Beans and not Servlets.
It really is more an architecture question as to whether you want to use Servlets for this kind of action. Or have a Servlet call an
EJB, and do the work there, the response won't return until the EJB is finished
Mark