Growing up in the post-television United States of America, there are only three great milestones in a teenager’s life, says film director Jason Reitman. “There’s an age where you’re allowed to drive, there’s an age where you’re allowed to drink, and there’s an age where you’re allowed to watch Saturday Night Live,” he says.

The third of those milestones refers to the country’s iconic sketch-comedy series – a patchwork of live set-ups, parodies and Weekend Update newsdesk segments – which has been a cultural monolith in American comedy for almost 50 years. A-list stars host it. And its political satire draws eyeballs from all over the world.

Saturday Night Live has also turned a long list of comedians into stars: Tina Fey, Will Ferrell, Kristen Wiig, Jimmy Fallon, John Belushi, Gilda Radner, Dan Aykroyd, Bill Murray, Eddie Murphy, Harry Shearer, David Spade, Julia Louis-Dreyfus, Amy Poehler, Chris Rock, Andy Samberg, Molly Shannon and Maya Rudolph among them.

“I remember those first few Saturdays that I was allowed to stay up and watch that show, and the thing that struck me the most was, I can’t believe they do this every Saturday,” Reitman says. “It felt so special. It felt like something that should only happen once a year, like the Super Bowl or the Oscars, and I couldn’t fathom that they did 90 minutes of new sketch comedy, and that it would be different every Saturday.”

There was Gilda Radner, whose parody of US journalist Barbara Walters – Baba Wawa – became one of the show’s mainstays. There was Betty White, who played baker Florence Dusty, who wrote the book on double entendre. And Aykroyd and Steve Martin, whose Two Wild and Crazy Guys were not remotely as attractive as they thought. And Weekend Update, which has seen many iterations, though it’s difficult to go past Fey and Poehler together.

As the show goes into its golden-anniversary year, Reitman, the 47-year-old Montreal, Quebec-born filmmaker, has turned his lens on its history, in particular the show’s opening night on October 11, 1975. It was, you may be surprised to learn, a Saturday. And while many of the show’s touchstone early moments spanned months, the film Saturday Night compresses them into a single night: the show’s opening night.

The director concedes he approached the project with enormous affection. “I knew this was going to be a love letter from the get-go,” Reitman says. “I found the process of interviewing all the original actors and writers and craftspeople and musicians to be an honour, and I was moved by the way they shared their memories with us. At that point, I just wanted to do well by it, and I wanted to make a movie that evoked exactly what it felt like to be there.”

The result is somewhat masterfully complex – a jangling assembly of moments and quirky opening-night disasters that seem, at every turn, almost certain to push the fledgling series off the air before it has even started. The film is also extraordinarily nuanced. Though the subject was flimsy, the film captures beautifully the uncertain and artistically magical nature of TV.

The narrative is tightly compressed: 93 minutes in official running time, including the credits, telling the story of the 90-or-so actual minutes prior to the show going, “Live from New York, it’s Saturday night!” There are glitches, disasters and even what feels like an orchestrated attempt by more conservative forces within the network to ensure it never makes it to air.

For an Australian audience, there is the added complication that, for most of its shelf life, Saturday Night Live did not air here. That does not take away from the natural conceit of ‘will they or won’t they get the show on air’, a tension wire that runs through the film. Indeed, this could be the story of Australia’s Norman Gunston. Or Graham Kennedy’s In Melbourne Tonight. Or our own iconic sketch-comedy series Fast Forward.

In fact, the film is stunning. The comic beats are almost perfect. And Reitman not only captures the camaraderie that propelled the show from a random pile of made-for-TV segments into an iconic cultural touchstone, he does so in a genuinely affecting manner. As insubstantial as TV can be, the stakes in Saturday Night are very real, and though the history books confirm the show did indeed make it to air, the film has some will-they-make-it white-knuckle moments.

“Comedians are essentially dark, sensitive human beings. That’s what makes them so damn funny,” Reitman says. “I felt like it was my job to capture what was going on through their heads and through their hearts, and not only their desires but their fears. And so the movie had to be a mix of people challenging each other, trying to make each other laugh and, simultaneously, their real search for identity as they pulled the show together.”

When the project went from idea to walking, talking motion picture, Reitman says he immediately contacted Saturday Night Live creator and (still) producer Lorne Michaels, to let him know the movie was happening.

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“When he heard the concept – 90 minutes to showtime on opening night – he really got that,” Reitman says. “He dug that idea and gave me his blessing and supported it. He didn’t weigh in on creative decisions at all on the movie. He heard the original idea, he got it, he supported it, and then was tickled through the rest of the process that it was happening.”

The film found a flawless Chevy Chase in Cory Michael Smith, and an unexpectedly brilliant Jim Henson in Succession star Nicholas Braun. (Braun also, bizarrely, plays Andy Kaufman.) Dylan O’Brien plays Dan Aykroyd, and Matt Wood is the legendary comedian John Belushi. And woven around them are Willem Dafoe as network executive David Tebet and J. K. Simmons as an insufferable Milton Berle.

For the role of Michaels, Reitman cast Gabriel LaBelle, who stunned audiences with his performance as aspiring filmmaker Sammy Fabelman in Steven Spielberg’s semi-autobiographical film The Fabelmans.

“What is great about this movie is you just fall into the trust of Jason,” LaBelle says. “He’s doing so much, and he’s so quick, he’s so funny. He can come up with a line that makes you laugh out loud when you just hear him pitch it to you, and you want to do right by him. You want to make his movie.”

The film, LaBelle adds, is deeply rooted in the reality – good and bad – that existed back then. “All your characters are just so present in their immediate environment,” LaBelle says. “There’s no reflection on their childhood or any big monologue that takes a stage where you breathe into it or anything. You are just reacting to what’s in front of you, and you just trust each other and move with it. It’s really fun to also just get out of your own head and trust that he knows what to do.”

The tight running time and single-thread story mean every element of the film has fought to win and hold its place, LaBelle says. “I think there is not a single moment of this film that doesn’t deserve to be in there. Everything tells a story. Everything is important to each character, and it all matters.”

What Saturday Night holds in balance beautifully is its moments of nostalgia. The moments, when they come, are tender without being overplayed. And nostalgia is a risky tool to play with.

“I feel like storytelling is always that tug of war between breaking barriers and being nostalgic,” Reitman says. “They are both of value and they are both core feelings. And it’s important to play with nostalgia because you need to play with what people know and what people have felt and what people understand, and it is just as important to try to do something innovative so that you are expanding on what the audience has felt before.”

One of the most unusual aspects of the film is that Reitman essentially shot it twice, the first time using stand-ins with the view that once he had road-mapped how he wanted to shoot the film, he could do so by leaning minimally on the cast and allowing the film to be shot more or less in time order.

“As I get older, I get more specific. I shoot less coverage,” Reitman says. “But more importantly, in this movie, the idea was for the audience member to feel like they just got dropped into the 1970s.

“So what I kept thinking about is: what is the audience member doing? Where are they walking? What are they looking at? What are they listening to? And we would design these shots as though you were really just walking through the hallways and up the stairs, and this chaos was happening around you.”

Ultimately, LaBelle says, the film is many things. “It makes you scared, it makes you laugh hysterically, it makes you emotional, it makes you happy, it makes you nostalgic, and it makes you hopeful for the future. There are so many things to this film.”

For LaBelle in particular, Saturday Night offered a compelling insight into how Reitman works. It also came to him after he had shot The Fabelmans with Spielberg, and another film, Snack Shack, written and directed by Adam Rehmeier, based on Rehmeier’s childhood in Nebraska.

“What I noticed about all three of these [filmmakers] is they’re making something that means a lot to them, and they’re working with the same crews they know they like – they’re working with their friends,” LaBelle says. “They’re humble, they’re funny, they’re kind, they’re gracious. They encourage you to be the best version of yourself that you can be.

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“I’ve worked with people who just lead with kindness, and that is a brilliant lesson. They are just radiating inspiration, and you just want to do them right because the writing is brilliant and their vision is brilliant and you feel grateful to be a part of it.”

That goes for the tangible and the intangible, Reitman adds. Which is not to say this was a haunted production but one full of “artistic ghosts”.

“Certainly when I was making Ghostbusters we were trying to capture the artistic ghosts, and I think that’s the same here,” Reitman says. “There’s something about hearing Cory Michael Smith say, ‘Live from New York, it’s Saturday night.’ There’s something about recreating some of these old sketches where you get to put on the clothes for a second.

“You feel it in the air, and it happens through chemistry,” Reitman says. “It happens because this cast, this ensemble, are so extraordinary, and they work so well together. It’s not that anyone individually is a standout; it’s that their chemistry creates magic, and it makes you feel like you’re back there, in the moment.”

Saturday Night is released in cinemas on October 31.

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