Not sure if this counts but I have done Star Wars Marathons were we watch all 6 movies. I did it successfully twice. Last time we tried it we had had enough after empire and bailed on Jedi. after that I didn’t try to do them all in one day.
I did successful marathons of the original trilogy many many times though.
During 9/11 I was compulsively channel hopping hoping that someone somewhere had actual information.
For the OP, most years we kept the fireplace channel on over a few days for Christmas.
This year I just turned on the fireplace instead.
MST3K Turkey Day, all day long (early 90s).
9/11 on CNN, for what seemed like forever.
Weather channel during Hugo.
CNN during opening bombing of Gulf War
Done plenty of the “turn on Headline News while doing a marathon stint of Civilization” many, many times. Up to the reader if that counts. 
When I was in grade school, MTV would run Daria marathons on weekends and I would find myself sitting there for a good 6-8 hours without realizing it.
I still refer to it as My Night from Hell™.
I was behind on my analytical chemistry lab book and pulling an all nighter in the dorm’s lounge to catch up. The cable didn’t work and the only channel the TV could receive was some weird UHF channel that played videos upon request. You made your request my dialing some 1-900 pay number…
And some heartless bastard apparently wanted an all night marathon of Lisa Stansfield’s All Around the World. The same video. On repeat. ALL NIGHT LONG. We stopped counting after 70+ repeats.
Sadly, we needed the noise to keep us awake. And it worked. And I still can’t stand that song.
When my business partner and I first started our company we would watch TVLand most of the day. When the second airing of Golden Girls came on in the wee hours of the morning, we’d crash for a few hours then get up and do it again.
I had just been released from the hospital after an appendectomy when Katrina hit. Being stuckon the couch for a couple days, I turned on the news and never turned it off for about 2 days. The whole thing was so incredibly overwhelming, and just when you thought you’d seen everything, more unsettling pictures would come in.
The Twilight Zone marathon on New Year’s Day. (But I would still change the channel during commercials.)
Now that’s a Business model I can do! 
Hah, I did that once. I think I was 13 (so 1986-7) and I decided to watch 24 hours straight of MuchMusic. I was so disappointed to discover that it wasn’t 24 hours of original programming but an 8 hour(?) loop.
A few years ago a truck crashed into a hydro pole near my work and knocked the power out so we all got to stay home. I spent the entire day on the couch cuddling my kitten and watching a CSI marathon on Spike. (The Las Vegas CSI, back in the Grissom days.) Best day off ever.
I remember watching most of the Planet of the Apes series as a marathon at least three times when I was a kid. On TBS, maybe? I used to also watch the “Bible movie” marathons, usually around Easter.
I also used to have the Olympics on non-stop when they would have things like gymnastics or ice dancing all day.
And there was a brief period of time in which I fancied myself a day-trader and would have Bloomberg on all morning…
When FXX was running every Simpsons ever last summer, I pretty much had my TV tuned to that nonstop except for a few hours here and there where I had something I needed to watch. I forget how long that was, but I know it was over a week.
Anytime there’s a major event like a hurricane or war bombings or whatever I find myself locked onto CNN just to see what’s going on and get every little bit of detail that I can.
STAR WARS!!!
I have watched 8 + hours in a row of professional wrestling
On any given Saturday college football comes on my TV at noon and ends at 2 in the morning or later
I may have some issues!
In 2000, the WWF started the pre-Wrestlemania stuff at noon, and didn’t end with the post-show stuff until around midnight, so I got you beat there.
Of course back in the era of the Monday Night Wars, I’d regularly be watching 5+ hours of wrestling every Monday, but that wasn’t all on the same channel.
A couple days, about 15 years ago there were twilight zone marathons on some channel, maybe sci, over new years eve. Now with netflix it isn’t necessary but I would watch those.
I had the flu during the Beijing Olympics and I couldn’t get off the couch for a couple of days. I think I had the games on the whole time. I developed an appreciation for water polo.
I was too drugged up to remember if it was the same station, but the last time I was in the hospital for awhile, I somehow ended up watching a lot of Lawrence Welk show. It was not all that unpleasant. 