@bradner Yes, technically he could but the problem is that ISP style routers have relatively low bandwidth capabilities. It's very easy to overload them with video traffic especially with a larger number of cameras. There is also no need to "route" traffic through a router because all camera traffic should be limited, and blocked, from needing access to the internet at all. A local time server takes care of time sync duties and updates should be downloaded, and applied, locally through the GUI of the camera.
Using multiple, smaller, PoE switches also eliminates a single point of failure. If one goes down for some reason the rest of the cameras can continue to operate normally on the additional switches.