Movies about tectonic cultural shifts tend to be too neat and tidy, too frictionless. “Saturday Night,” director Jason Reitman’s fictional reimagining of the debut of “Saturday Night Live,” is a nice, safe movie about a revolution. Busily plotted and sporadically funny, it is a backstage look at the night a gang of comics whom most of the world had never heard of began taking over TVs across the country. It was a comedy home invasion on a national scale, and it was glorious (when it didn’t suck).

The movie, written by Reitman and Gil Kenan, has a straightforward conceit. It opens at Oct. 11, 1975, the night that the show, then called “NBC’s Saturday Night,” is scheduled to debut. (The name was changed in 1977.) In just 90 minutes — ticktock — the show will go live if the performers, writers, crew, network suits and some guy named Lorne can get it together in time. A lot of money, reputations and possibly bright futures are riding on the show, but with its deadline looming, it still seems underbaked and, from some vantage points, overly abstract.

To convey that premiere and what it portended, Reitman both sticks to the historical record and embellishes it, building momentum by zeroing in on some minicrisis amid rapid edits, swish pans and rushing bodies. Everything and everyone at 30 Rockefeller Plaza runs too fast or seems immobilized, with characters either in frenetic motion or huddling in pools of flop sweat. As the minutes pass, Reitman periodically cuts to a clock on screen or someone calls out the time; at one point, a set designer, Leo Yoshimura (Abraham Hsu), slowly begins installing bricks on the stage of Studio 8H, each brick an emblem of the show’s parts sliding into place.

In a (real) 1975 news release, NBC called the show “a new concept in late-night programming.” The network wanted a replacement for weekend reruns of “The Tonight Show Starring Johnny Carson,” and this venture was going to be a comedy show with sketches, musical guests, short films and the Muppets. But it was unclear what it was, maybe even to those behind the scenes. That much seems obvious when an NBC executive, Dick Ebersol (Cooper Hoffman), asks the show’s creator-producer, Lorne Michaels (Gabriel LaBelle), if he knows what it is. The straight-faced Lorne responds with an amusing, self-aggrandizing analogy involving Thomas Edison, the light bulb and electricity. Who are you in this metaphor, the baffled exec asks.

Lorne doesn’t answer, but the movie does by making him its focus. The character is less interesting than his surroundings — he’s more a blurry place holder than a fully realized personality — but whether here or there, Lorne is the center of this storm. He’s the hub, the visionary, the guy who can see past the chaos. Sure, there’s his wife, writer Rosie Shuster (a tart Rachel Sennott); the host, George Carlin (Matthew Rhys); and a creepy suit, Dave Tebet (Willem Dafoe, in by far the funniest turn). But the star is Lorne because even genius apparently needs a boss.

So, hi, Chevy Chase (Cory Michael Smith), Gilda Radner (Ella Hunt), Jane Curtin (Kim Matula), Laraine Newman (Emily Fairn), Dan Aykroyd (Dylan O’Brien), Garrett Morris (Lamorne Morris, no relation) and John Belushi (Matt Wood). It’s nice to see them, so it’s too bad that only a few of the actors playing the main cast — and only the men — manage to register. That’s the case even when Reitman gestures at the show’s gender problems, as in a peek at a still-funny sketch about female construction workers learning how to harass a guy in short shorts. It’s Dan’s squirmy embarrassment — and how he then wags his rump — that makes it work.

Reitman does better when he takes on the show’s racial homogeneity, largely by foregrounding Garrett. Long the only Black cast member, the real Garrett Morris held his own despite some ghastly treatment, which, in the movie, his fictional counterpart expresses by belting, “I’m going to get me a shotgun and kill all the whities I see.” Michaels helped write the song, and Garrett Morris sang it while wearing prison stripes in a later episode for a sketch set in prison.

“Saturday Night” is a movie made by fans, but because Reitman assumes that his viewers are fans, too, and because he’s racing against the clock, he gestures at instead of digging into the show, its humor and history.

He nods at the generational shifts in comedy and TV, and tweaks the censors. Yet, there’s not enough about how the show’s comedy works, and why one sketch kills and another dies. And there’s no sense of how it works as television.

The medium’s intimacy can make you feel as if you’re in on the subversion, although nothing can prepare you for the destabilizing conceptual genius of Andy Kaufman (Nicholas Braun) lip-syncing — to you, in your parents’ home! — the theme of an old cartoon you watched as a child.

It’s agreeable hanging again with Kaufman, however adulterated this version is. The same holds true of the rest of the crew, even if it’s often like watching children play dress up at a party.