One does not know what took so long for drag performer/singer, writer and activist Taylor’s Mac‘s Olympian undertaking, “Taylor Mac’s 24-Decade History of Popular Music,” to make it to TV and the masses.

An epic 246 song show, toured as four six-hour marathon productions, he only did the entire 240 year history — with band, back-up singers and guest musicians — in one long day and night on one occasion — Oct 8-9, 2016.

Filmmakers Rob Epstein and Jeffrey Friedman, who gave us “The Celluloid Closet” and “Linda Ronstadt: The Sound of My Voice,” and their filming/recording production crew were at St. Anne’s Warehouse in Brooklyn to capture it all.

Maybe it took them this long to edit 24 hours of straight-through performance — with interview inserts with the production team and showcasing the outlandish, period-parodying costumes of designer Machine Dazzle at a fashion shoot — into a finished film.

In any event, the timing of this history lesson through music presented in a drag show could not be better — released right before July 4, right in the middle of nationwide attacks on drag, sexuality and history itself by a zealous, scapegoating, intolerant minority.

The show was born during that live-performance/Youtube-immortalized “History of Rap,” “History of Dance,” “History of Music” craze of the mid-to-late 2000s.

Mac’s brainchild? To tell the long, sometimes tortured tale of the United States via music, the popular songs of every era, “songs you’d hear in pubs (mostly).” He’d include what would later be called the “erased” parts of our national story and fold it all into an AIDS allegory.

“That history is in our songs,” he says on stage, midway through a vamp on “Yankee Doodle” to open the show.

So he was going for “epic,” an “Angels in America” drag musical that would highlight the nation’s history and the queer elements and famous figures — like Walt Whitman — and unknown ones.

“Bayard Rustin, a queer Black man, organized the (1963) March on Washington,” is among them.

The filmmakers turn this “You had to be there (the committed-to-the-end audience was relatively small)” show into Taylor Mac’s “The Last Waltz,” a generous sampling that gives us the musical, theatrical, historical and emotional flavor of the event.

I can’t imagine sitting through any production of that length. But this 106 minute sampler zips by, serving up facts you didn’t know — “Coal Black Rose,” the first “minstrel” (singer in blackface) song, started life as a racist sea chantey about gang rape of a slave — and old tunes rendered in new lights.

“Father of American Song” Stephen Foster is ripped for his racist-even-for-their-day ditties. Ted Nugent’s anti-glam rock “Snakeskin Cowboys” is “appropriated” from its “f-g-bashing” origins and rendered into a “Junior Prom” ballad.

Bowie’s “Heroes” to Bruce’s “Born to Run” — “So that’s what it was like in America before ‘Will & Grace!'” — take on renewed cultural significance, placed here on Mac’s historical timeline.

AIDS is summed up as a disease, a disaster and a call to arms — out of the closet and into the streets — as Laura Brannigan’s dance-club hit, “Gloria,” performed by Mac in an exhausted, funereal ballad that morphs into audience participation “community building.”

Mac, a MacArthur “Genius” grant recipient, holds center stage for almost the entire “performance art” concert and theatrical happening, with spirited backup singers, singing harpist Erin Hill (“10,000 Miles”) or folk singers taking on a number, here and there.

Even though I couldn’t imagine the endurance contest of experiencing the show in person in real time, this documentary — which identifies via graphics the songs and their earlier-than-you-realized dates of composition — leaves you wanting more. As dazzling as this highlights sampler can be, one hopes more of it will be released in bite-sized servings.

Perhaps on Youtube, where this sort of performative history with social commentary and comical interjections first reached a mass audience? We’ll see.

For now, we have an excellent snapshot of a singularly sensational theatrical event, entertainingly pulled off-by a talent who should be as celebrated for his stamina — He’s OK with “He,” but identifies as “Judy.” — as he is for his genius.

Cast: Taylor Mac, Matt Ray, Anastasia Durasova,
Niegel Smith

Rating: unrated, profanity, sex toys and phallic props

Credits: Directed by Rob Epstein and Jeffrey Friedman. An HBO release on Max (June 27).

Running time: 1:46