There’s an existential question that runs throughout “Saturday Night,” Jason Reitman’s love letter to the iconic “Saturday Night Live,” and its chaotic entry into the world Oct. 11, 1975. People keep asking the show’s creator and producer, Lorne Michaels (Gabriel LaBelle) what, exactly, the show is? It’s a question he’s not able to answer until nearly the end of the movie.

The film takes place over the course of the 90 minutes leading up to the first show and utilizes an ominous ticking clock to count down the minutes until showtime. Over that time, whatever can go wrong already has, will, or is in the process of going wrong, swirling around the preternaturally calm eye of the storm, Lorne.

The existential question of what this show is or will be thrums underneath the constant churn of crisis that Lorne attempts to manage: Will Belushi (Matt Wood) sign his contract? Will NBC executive David Tebet (Willem Dafoe) throw to a Johnny Carson rerun? How should Lorne’s estranged wife Rosie (Rachel Sennott) be credited? Can they find a lighting designer?

Reitman, who co-wrote the script with Gil Kenan, has said that he was inspired by a short stint guest-writing on “SNL” to structure this 50th anniversary tribute film around the 90 minutes before the show goes on air. Based on interviews with those who were there, the film is a cavalcade of stars, both in the actors playing now familiar faces (Cory Michael Smith as Chevy Chase, Dylan O’Brien as Dan Aykroyd, Ella Hunt as Gilda Radner), and in a couple of high-profile actors making appearances as TV legends (Dafoe; J.K. Simmons as Milton Berle). Comedy nerds will delight in the presence of writers like Alan Zweibel (Josh Brener), Al Franken (Taylor Gray) and Herb Sargent (Tracy Letts).

But Reitman and the talented young cast manage to make “Saturday Night” much more than just young actors having fun in bell-bottoms and wigs. Shot on Super 16mm by Eric Steelberg with an antsy, roaming camera that swoons and zigzags up and down the hallways of 30 Rock, peering into dressing rooms and ping-ponging back and forth between the determined Lorne and his doubting partner, Dick Ebersol (Cooper Hoffman), there’s a wild, stimulant-addled energy to the film that is only enhanced by Jon Batiste’s jittery-jazzy score of piano and percussion (the musician also appears as musical guest Billy Preston).

“Saturday Night” is enormously entertaining and at times excessively busy, though a few bright spots emerge from the crowd, delivering real performances. Smith is astonishing as Chase, seemingly channeling him, and LaBelle, one of the most exciting young actors to come along in a long time, steadily and earnestly holds the center as Lorne, somehow remaining steadfast in his belief that the show will, and must, go on.

As Lorne tries to explain the show to a group of NBC executives, he says that it’s television by and for the people who grew up on it. It’s a generational shift from the vaudeville roots embodied by Berle. He’s attempting to capture lighting in a bottle, to both create culture and reflect it back to the audience, to throw something at the wall and see if it sticks. That such a revolutionary program came about as the result of a contract dispute between NBC and Carson, only makes it all the more magical that it even exists.

Though “Saturday Night,” the film, feels ephemeral and somewhat fleeting, it represents something that has endured, and continues to, through the sheer force of will that is Lorne Michaels.

MPA rating: R (for language throughout, sexual references, some drug use and brief graphic nudity)

Running time: 1:49

How to watch: In theaters