"or my edification,,,,is there a specific reason for the ".5.1" as a standard of some sort?"
Not that I know of as a fellow user. Not as a standard. I'm not sure how you ended up with that IP address for the Dlink router. Did the TWC cable guy go into the router and configure anything? If so, he may have changed it so that it would be different than the IP address for the modem.
I'm not familiar at all with Ubee or Dlink, but for some other modem brands the IP used to access the modem is 192.168.100.1. I don't know if that is the case for Ubee; I simply don't know if it is standard for you to access your modem via 192.168.0.1 like you currently are. Of course, you want to be sure the cable guy did indeed put your modem into the correct mode for your equipment situation and that he did disable the wireless routing component.
Maybe a Ubee user with a modem and separate router setup similar to yours will comment here with more info on what the 2 IP addresses should be and how to check the equipment configuration. Or you could start a new thread and specifically ask that question. Good luck!