Unless you move or change cable companies/services, never.
Unfortunately, sometimes the new channels seem to take a couple of extra days to show up on cable card systems. One thing you can TRY it to completely unplug your tuning adapter and Tivo for about 15 minutes, then power the tuning adapter up first, and once it's going, plug the Tivo back in. MIGHT work.The reason I'm asking is because comcast was to add "HD Net" on June 30th to my comcast system but when I go to the channel "It say's Channel not available but TIVO added the listings.