Ok, it looks like the delay is caused by the UPnP logic. If I remove the UPnP attempt and just use the NAT-PMP code it completes within 2-3 seconds.
I tried updating to the latest UPnP library source code, but the delay is still present.
It looks like things do eventually settle down with 5 cameras, but it can take up to 30-60 seconds to do so. After you let it run for that long, I am guessing that everything looks good, and you are able to connect to all of your cameras, is that correct?