Labor Day weekend brings an intimation of changing seasons, and we’re not talking about the weather. The launch of the new TV season already has begun on Fox, and the launch of a new mini-network (MYNetwork) is only days away.

Dennis Haysbert (“The Unit”) narrates “A Day in the Life of Television: A Museum of Television & Radio Special” (7 p.m. today, CBS), a behind-the-scenes look at the production of a variety of shows, including “Everybody Hates Chris,” “ER,” “The Simpsons,” “CSI” and “Entertainment Tonight.”

The network will follow this 90-minute ecumenical celebration of the medium with a more blatant plug for its new products, the “CBS Fall Preview” (8:30 p.m. today, CBS). Recent Emmy winner Julia Louis-Dreyfus (“The New Adventures of Old Christine”) will host. Not to be outdone, “NBC Primetime Preview” (7 p.m. today, NBC) also shows off that network’s new lineup.

¢ What is it about Camelot that brings out pretentious language and stilted cliches? Sam Neill portrays the legendary wizard in the original TV movie “Merlin’s Apprentice” (7 p.m. today, Hallmark). Merlin begins the movie by taking a nap that turns into a 20-year slumber. When he awakens, the enchanted kingdom is in the grip of darkness. And “Apprentice” is in the thrall of what seems like a 20-minute muffled voiceover from the bewildered Merlin.

¢ One of the more notable of the many documentaries to mark the fifth anniversary of Sept. 11, “What Really Happened Inside the Twin Towers” (8 p.m. Sunday, Discovery) uses interviews, re-enactments, archival footage and computer-generated imagery to provide viewers with a minute-by-minute account of the confusion and heroism in the short time between the time the terrorist’s jets hit the buildings and their unexpected collapse.

Like the two TV movies and one feature film about Flight 93, this feature lies somewhere between the dramatically unforgettable and the emotionally unendurable. Every time a new 9-11 project is announced, people tend to ask, “Is it too soon?” I think the more apt question might be, “Is it too much?”

¢ “The Jerry Lewis MDA Telethon” (Sunday, check local listings) has been a Labor Day TV tradition since 1966, when it aired on one lonely New York station and raised $1 million. To put that into perspective, it aired Sept. 5, 1966, a week before the premiere of “The Monkees” and two months before Ronald Reagan was elected governor of California. Donovan’s “Sunshine Superman” was the No. 1 song on the Billboard hit parade.

Today’s highlights

¢ Georgia Tech hosts Notre Dame in college football action (7 p.m., ABC).

¢ Fans have chosen their three favorite episodes of “Sue Thomas: F.B.Eye” (7 p.m., i) to run consecutively.

Sunday’s highlights

¢ NASCAR action (7 p.m., NBC) from California Speedway in Fontana, Calif.

¢ City dwellers rise from the ashes on “Extreme Makeover: Home Edition” (7 p.m., ABC).