1gig router means nothing when it comes to these cameras.
If you unplug the router and your BI computer cannot see the cameras, then that is usually the issue.
That delay is probably a result of everything going thru the router. I dual NIC and it is pretty instantaneous.
Cameras connected to Wifi routers (even if the cameras are hard-wired) are problematic for surveillance cameras because they are always streaming and passing data. And the data demands go up with motion and then you lose signal. A lost packet and it has to resend. It can bring the whole network down if trying to send cameras through a wifi router. At the very least it can slow down your entire system.
Unlike Netflix and other streaming services that buffer a movie, these cameras do not buffer up part of the video, so drop outs can happen and usually get worse over time as dropped packets are lost and accumulate. You would be amazed how much streaming services buffer - don't believe me, start watching something and unplug your router and watch how much longer you can watch NetFlix before it freezes - mine goes 45 seconds. Now do the same with a camera connected to a router and it is fairly instantaneous (within the latency of the stream itself)...
The same issue applies even with the hard-wired cameras trying to send all this non-buffer video stream through a router. Most consumer grade wifi routers are not designed to pass the constant data stream data of cameras, and since they do not buffer, you get these issues. The consumer routers are just not designed for this kind of traffic, even a GB speed router.
So the more cameras you add, the bigger the potential for issues.