I believe I'd install the card when it's requested in the guided set-up, Comcast in some areas has a separate "cable-card" channel line-up. My area does for sure.
I was transferring a card from another machine to the new machine and everything went well. I have no premiums so I disregarded the call for repairing and I've complete access to everything I subscribe to.
Will a "fresh card" have functionality without the call? I don't know. If it was attached to your account by the office when you picked it up, maybe!
The Tivo support mentions connecting it first for a couple days I believe but then in the install they mention doing it when when requested in the guided set-up. I believe their assumption is that the purchase is a "first" and you don't have the card in hand!
I assumed since you mentioned the HD that you're NOT transferring the card but have a "fresh" card in hand.
I would ignore the opening paragraph here and just proceed by the numbers!