We are at the apex of “Saturday Night Live” appreciation. Now entering its 50th year, “SNL” has never been more unquestioned as a bedrock American institution. The many years of cowbells, Californians, mom jeans, Totino’s, unfrozen caveman lawyers and vans down by the river have more than established “SNL” as hallowed late-night ground and a comedy citadel.

So it’s maybe appropriate that Jason Reitman’s big-screen ode, “Saturday Night,” should arrive, amid all of the tributes, to remind of the show’s original revolutionary force. Reitman’s film is set in the 90 minutes leading up to showtime before the first episode aired Oct. 11, 1975.

The atmosphere is hectic. The mood is anxious. And through cigarette smoke and backstage swirl rushes Lorne Michaels (Gabriel LaBelle), who’s trying to launch a new kind of show that even he can’t quite explain.

“Saturday Night,” which opens in theaters Friday and expands in the coming weeks, isn’t a realistic tick-tock of how Michaels did it. And, while it boasts a number of fine performances, I wouldn’t recommend it for anyone hoping to see an illuminating portrait of the original Not Ready for Prime Time Players.

No, Reitman’s movie is striving for a myth of “Saturday Night Live.” Michaels’ quest in the film — and though he never strays farther than around the corner from 30 Rock, it is a quest — is not just to marshal together a live show on this particular night, it’s to overcome a cigar-chomping old guard of network television. (Milton Berle is skulking about, even Johnny Carson phones in.) In their eyes, Michaels is, to paraphrase Ned Beatty in “Network,” meddling with the primal forces of nature.

In mythologizing this generational battle, “Saturday Night” is a blistering barn-burner. In most other ways (cue the Debbie Downer trombone), it’s less good. Reitman, who penned the script with Gil Kenan, is too wide-eyed about the glory days of “SNL” to bring much acute insight to what was happening 50 years ago. And his film may be too spread thin by a clown car’s worth of big personalities. But in the movie’s primary goal, capturing a spirit of revolution that once might have seized barricades but instead flocks to Studio 8H, “Saturday Night” at least deserves a Spartan cheer.

A clock ticking down to showtime runs as ominously as it might in “MacGruber” throughout “Saturday Night.” Nothing is close to ready for air. John Belushi (Matt Wood) hasn’t signed his contract. Twenty-eight gallons of fake blood are missing. And, most pressing of all, the network is poised to air a Carson rerun if things don’t take shape. An executive pleading for a script is told, “It’s not that kind of show.”

What kind is it? Michaels, himself, is uncertain. He’s gathered together a “circus of rejects,” most of them then unknown to the public. There is Gilda Radner (Ella Hunt), Chevy Chase (Cory Michael Smith), Garrett Morris (Lamorne Morris), Jane Curtin (Kim Matula) and Dan Aykroyd (Dylan O’Brien). Also in the mix are Jim Henson (Nicholas Braun), who spends much of the movie complaining about the untoward things the cast has been doing to Big Bird, Andy Kaufman (Braun again), Billy Crystal (Nicholas Podany) and the night’s host, George Carlin (Matthew Rhys).

Most of them pass too quickly to make too much of an impression, though a few are good in their moments — notably Smith, playing up Chase’s braggadocio, O’Brien and Morris. Garrett Morris, the cast’s lone Black member, is in a quandary over his role — because of his race and because he was a playwright before being cast. Though “SNL” was revolutionary, it hardly arrived a finished product. Morris here is a reminder of the show’s sometimes — and ongoing — not always easy relationship to diversity, in race and gender.

It also wasn’t always such a break from what came before. When Chase faces off with Berle in a contest over Chase’s fiancee, Jacqueline Carlin (Kaia Gerber) — one of the movie’s few truly charged scenes — they seem more alike than either would like to admit.

It’s not a great sign for “Saturday Night” how much better the old guard is than the young cast. Along with Simmons’ Berle is Willem Dafoe’s NBC executive David Tebet. He provides the movie its most “Network”-flavored drama, seeing “a prophet” in Michaels and, despite wavering skepticism, urging him to be “an unbending force of seismic disturbance.” Also in the mix — and a reminder that the suits had newbies, too — is Dick Ebersol (a refreshingly genuine Cooper Hoffman ), a believer in Michaels but only up to a point.

Ultimately, this is Michaels’ show, and he’s played winningly by LaBelle, the “Fabelmans” star, even if the characterization, like much of “Saturday Night,” is a little thin. Sometimes by his side, as he races to get the show ready is the writer and Michaels’ then-wife, Rosie Shuster (the excellent Rachel Sennott), who you want more of.

It seems to be an unfortunate truth that dramatizations of “Saturday Night Live” inevitably kill it of laughter. That’s true here just as it was in Aaron Sorkin’s “Studio 60 on the Sunset Strip.” The exception to that, of course, is Tina Fey’s “30 Rock,” which was smart enough to abandon all the “SNL” mythology and focus on what’s funny.

This “Saturday Night” may have a legacy of its own; a lot of this cast, I suspect, will be around for a long time. And, ultimately, when the show finally comes together, it’s galvanizing. The cleverest thing about Reitman’s film is that it ends, rousingly, just where “SNL” starts.

“Saturday Night,” a Columbia Pictures release is rated R by the Motion Picture Association for language throughout, sexual references, some drug use and brief graphic nudity. Running time: 108 minutes. Three stars out of four.