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Counting down the minutes before the premiere, Producer Lorne Michaels (Gabriel LaBelle) has to juggle network brass, an unfinished set and a wild cast of performers before he can even think of shaping the elements into a 90-minute variety show.

The year is 1975 and, inherent in that, a lot of “older� execs hoping this replacement for “Tonight Show� reruns will fail.

New to the game, Michaels over-schedules his show, so acts that don’t get on (including Billy Crystal, who later became a cast member), wait and wonder. John Belushi (Matt Wood), the Brando of the bunch, is as aloof as actors get. He won’t sign his contract, and he doesn’t want to wear a bee costume. Garrett Morris (Lamorne Morris) wonders why he’s on the show (and gets a great laugh with a quick song that later becomes a skit) and what kind of work it’ll eventually be.

Dan Aykroyd (Dylan O’Brien) runs interference backstage while Chevy Chase (Cory Michael Smith) wows the affiliate heads who’ve stopped in to watch this thing emerge. The three female cast members (true to form) don’t get much screen time, but Rachel Sennott (as the smart, insightful writer Rosie Shuster) dominates as the one who can get it all on track. She gets great lines, too, and the kind of credit that wasn’t passed around much five decades ago.

Think “My Favorite Year� and you’ll get an inkling of what “Saturday Night� is all about. Director Jason Reitman lets a clock be his guide. It shows how much can happen before the show goes on the air.

While Aaron Sorkin tried to do the same thing with “Studio 60 on the Sunset Strip,� he didn’t quite have the manic quality that this does. Obviously heightened, the action pulls you into that dark world of comedy and prays you can make it out on the other side.

LaBelle does a great job wending his way through the chaos, but Smith is the real scene stealer, able to capture some of Chase’s split personality in mere minutes. Like O’Brien, he has enough of the tics and vocal mannerisms to make you believe you’re seeing the real thing. When J.K. Simmons shows up as Milton Berle, the impersonation game kicks into high gear.

George Carlin (Matthew Rhys), Andy Kaufman (Nicholas Braun) and Jim Henson (also Braun) flesh out the parade of talent. They’ve got questions for Michaels. He, however, has that ticking clock.

The idea that “Saturday Night� (it added the “live� years later) was revolutionary gets lost a bit in the translation. Berle and a network suit (nicely played by Willem Dafoe) are the only real barriers, even though Dick Ebersol (Cooper Hoffman) emerges as the only old-school force in Michaels’ operation.

A treat for everyone who saw those early years, “Saturday Night� explains why some weeks are good and others aren’t. It also salutes the miracle of live television and the masterpiece Michaels created.