A big selling point for pitching digital video recorders is the time-shifting option they offer for watching more TV shows. The thing is, that viewing time ultimately has to be shifted somewhere, and that “somewhere” increasingly ends up being at the end of the day/week:

With one-third of American TV households now equipped with DVRs like TiVo, the 10 p.m. hour is emerging as a popular time for people to catch up on what they missed earlier in the evening, or earlier in the week.

Here’s some math: NBC has lost an average of 1.8 household ratings points at the 10 p.m. hour compared to fall 2008, according to the Nielsen Co. At the same time, DVR usage — which is also measured by Nielsen — is up by 1.4 points in that hour.

“The DVR phenomenon is a little bit higher than we thought,” said David Poltrack, CBS’ chief research executive.

For example, many people watch CBS’ “CSI: Crime Scene Investigation” Thursdays at 9, tape ABC’s “Grey’s Anatomy” at the same time, then watch the medical soap an hour later, he said. They may tape “The Mentalist” (Thursday at 10) for later viewing. One casualty of growing DVR usage is that Friday nights, home of “Medium” and “Ugly Betty,” are becoming a TV wasteland because so many people are catching up on programs they missed during the week.

Anecdotally, I’ll buy this breakdown. From what I observe from my modest Twitter following group of 500 and change, I notice recurring tweets during late night and the weekend from people obviously filling up on a week’s worth of DVR recordings.

I’m not on this television catch-up ride, because not only don’t I have a DVR, but I also watch nothing in the way of original series programming. My main onscreen consumption is sports, and while I could record the week’s hockey and football for more convenient viewing, I’m old-fashioned enough to shortchanged if I’m not watching a game live. Plus, any backlog of recordings smacks of a sort of homework assignment to me, so I’d rather pass up the original broadcast window rather than be compelled to watch something in my spare time.

But I’m fascinated by the trending on display. This was what was supposed to happen when the VCR hit the market 25 years ago. The difference this time around is as simple as the hardware: No fumbling with tape cassettes (sidenote: I’m amused by the AP reporter above still referring to DVR recordings as “taping”). DVRs have automated the process more-or-less completely, so that casual users only ever have to work the remote control.

The upshot of this is that, of course, the 10PM slot and most/all of Friday primetime is a challenge for original network programming. It makes you wonder why NBC is so big on “The Jay Leno Show” to occupy five days’ worth of late-primetime slots. Could they not have seen this viewer-habits trending forming a year ago? Or did they see it, and still gambled on the combination of Leno’s appeal and lower production costs carrying the day? Either way, at this rate, the Peacock Network might as well consolidate the losses by making Fridays “Jay Leno Day”: Run marathon five-hour episodes of the show from 6-11PM. Since everyone is playbacking their DVRs at that time anyway, nobody will notice the resultant sucking sound of that broadcasting black hole…