Delayed TV viewing: from C3 to C7

Thanks to Digital Video Recorders (DVR, such as TiVo) TV audiences are shifting their viewing. Should advertising measurement take into account what is watched after the first broadcast?  How many days? 3 days, 7 days? 30 days? More? For the time being, C3 (live plus 3 days) is the standard, but GroupM (WPP) has agreed to use C7 to buy commercial time on TV networks (upfront market).
This difference in definition and metrics is important for TV channels. Fox did some transactions using C7 ratings for the upfront market in June 2014.

For a long time, the shifted audience (VCR) was not measured and therefore not paid for by advertisers; it consequently did not generate any revenue: it was like a bonus. Going 7 days would increase revenue for the networks (only for those with successful programs, mainly the big networks like CBS) and decrease the cost of TV advertising (lower CPM's), making some programs more competitive.
DVR penetration, according to Nielsen, is close to 50% of American TV households. In the long run, as DVR equipment and VOD become more important, a longer delay period could become significant. How long a delay?

TV is trying to recapture its unmeasured scattered audiences: out-of-home audiences, VOD, shifted, online, mobile, etc.: all in all, about a third of the total TV audience is not sold (see, for CBS: Les télévisions d'une émission).

See also, in French, on this blog:

• "Le différé fait de l'audience"
• "Les télévisions d'une émission"