[Exim] poor man's teergrubing

I'm considering adding delays to acl_check_rcpt for blacklisted hosts and for
invalid local recipients. Any idea what reasonable values would be? I don't
want to reject blacklisted hosts outright since the blacklist could be wrong.

warn    message = X-Warning: $sender_host_address is in a black list at
$dnslist_domain - $dnslist_value
         log_message = found in $dnslist_domain - $dnslist_value - $dnslist_text
         hosts = !<local netblock>
         dnslists = relays.ordb.org : \
                 relays.visi.com : \
                 sbl.spamhaus.org : \
                 list.dsbl.org : \
                 dnsbl.njabl.org : \
                 bl.spamcop.net
         delay = ???

   accept  domains       = +local_domains
           endpass
           message       = unknown user
           verify        = recipient
           delay         = ???

Are these the correct locations for the delay statements? Do I have to split
the second condition (accept/deny) to get this to work?
Thanks,
John