The programming and viewing habits of the last 50 years — exemplified by the checkerboard of competing programs on the broadcast networks — are being replaced by an Internet-influenced time-shifting model of scheduling. As a result, the very definition of prime time may be changing…

The irrelevance is partly because of digital video recorders, the bane of many a television executive. Viewers in the 28 percent of homes with DVRs are recording programs at 8 and 9 p.m. and playing them back later in the evening, hurting the 10 p.m. hour. Of the 10 prime-time programs that gained the biggest audience from DVR usage this year, none were on at 10 p.m…

Due in part to time-shifting, many viewers, especially the younger ones who are prized by advertisers, do not know what is on at 10 p.m. And they increasingly do not care. There is a simple test of this scheduling shift: just ask a friend what time “Dateline NBC” is broadcast. The hard-to-remember answer is Friday nights at 10 — but not for long.