The default proxy check timeout is 30 seconds. The default cache time is 30 minutes. This is the time that we hold a user before letting them on the server. If the dnsbl doesn't answer in this amount of time the user is allowed on the server. If later we do get a hit from the dnsbl the user on that address will still be killed and banned from the server.
/as security DNSBL XBL set timeout 5