Earlier quoted context omitted.
One thing that is certain is that there are more commercials now. If you watch an episode of The Big Bang Theory sans commercials, you will notice that it is only 17 minutes long! And that includes the 60 second intro. So 13 minutes of commercials for 16 minutes of actual content. No chance I'll be going back to regular TV.
Is that all that different from what it was before? My recollection of 80s sitcoms & children's programs is that they had 3 commercials of 3 minutes apiece, plus a 3 minute break between programs. That's 12 minutes. Actually, I can test this...I've got some old My Little Pony episodes lying around on a hard disk. They're 9 minutes apiece. IIRC they ran 2 to a timeslot, so that's 18 minutes of show per 30 minute times…
When I was in High School, our English teacher actually wrote and produced a TV show and was telling us about her experience and some of the things she had to do to cut episodes in the right amount of time for commercials. At the time (mid 2000s), the average was 23 minutes of show per 30 minute episode.
Looking across my library at recent shows, it seems to average about 21 minutes nowadays.