in this scenario, you have a router/modem combo with dhcp enabled. no control over dhcp, but this router seems to always assign the same ip address to the same devices. lets say the router assigns 192.168.0.27 to a local machine. you, in turn, set a static ip address on said local machine as 192.168.0.27. in this scenario, and, well my situation, you still have access to the network.
i understand that the router will expect the local machine to operate under that name until the timer runs out and then its open game. will it stop accepting traffic from the local machine under that address when the timer runs out? if no device ever receives that ip address, would it ever really be an issue?
Well, the answer is - as usual - "it depends", but in most cases it will just work fine. Being DHCP-enabled does not mean "DHCP only" and most home routers I know about will just let those statically addresses work. There might be some which don't let them work because the address is in the pool the have "authority over" - but these should be the minority.