When wearing their nun costumes, Mark McCloughan and Jaime Maseda can be mistaken for twins. So, in their performance piece Abbot Adam: Matins/Lauds, their dialogue about the inner lives of medieval nuns is like a meeting of alter egos. It's a welcome, unifying element.

Without altars, egos, or religious artifacts elsewhere in this sprawling, garrulous piece, audiences need an anchor as to what's going on here and what the performance actually is.

The all-night-long performance piece is scheduled to run for six hours at the Barnes Foundation starting at 11:59 p.m. Saturday following two overnight live-streamed installments Thursday and Friday. It straddles many genres, according to the two performers collectively known as No Face Performance Group. Previous installments have been seen in Philadelphia in recent years at places such as FringeArts.

McCloughan and Maseda are genuinely keen to explore lives inside a medieval cloister and address each other with the antiquated formality of "thee" and "thou." Yet both of these guys in their late 20s have beards, wear glasses, freely consult their laptops, and change clothes in front of the streaming-video camera, revealing 21st-century underwear. It's fly-on-the-wall theater, allowing audiences to witness highly personal experiences in real time. But it's also an art installation that feels little need to entertain in the usual sense.

"We may swerve toward the satiric or the absurd, but that's not the primary mode of our engagement," said McCloughan.

"Obviously, we're going to ruffle somebody's feathers at some point," said Maseda, "but at the heart of this, we're devoted to this material and not doing some surface-level farce."

The pair have been working together since 2007, having first met at Wesleyan University in Connecticut and later done apprenticeships at Philadelphia's Pig Iron Theatre Company. Their unseen godfather is the late Charles Ludlam — famous for the proto-queer Ridiculous Theatrical Company in 1980s New York — who performed great characters of classic theater with camp in one act and complete sincerity in another. In the foreground is the No Face fascination with things medieval: This new piece is the third in a series of monastic-centered works that began in 2014, this one dealing with the nexus of divine vision and earthly life experienced by nuns.

"As research, we've been reading the Decameron," a 14th-century collection of short stories, said Maseda, "which is a kaleidoscopic view of high tragedy and courtly love." Modern anachronisms keep the presentation from being a re-enactment. Rather, it's a reflection of their own monastic-style all-night work sessions.

Though audiences are encouraged to come and go in the six-hour Saturday performance — blankets and sofas are available for napping at the Barnes — there's something to be said for staying for the duration in keeping with the rigorous sleeping, waking, and praying schedule that helps viewers to enter the monastic mindset. "It's a single, long-form improvisation," said McCloughan.

As theater, the Thursday streaming (marred by some signal-failures on my end) was low-tension and casually paced, with discussions about open-ended issues, such as the nature of vanity and shadows. Sometimes, I watched them sleep (though only briefly). Music ranged from medieval chant to club music. The dawn finale — which I missed due to my own sleep needs — is said to have greater theatrical density. And the delirium? I only saw visionary dreams, first experienced and then recounted.

Some good lines periodically surfaced: "Are we keeping the outside world away? Or are they keeping us in?" This is an ongoing issue here: Monastic life might seem like a prison sentence to the outside world, but inside, it can feel like a liberation from real-world cares and complications. But as agents of prayer — pure and simple — the nuns in the performance piece also seem self-obsessed with, among other things, the inner workings of their bodies. There were also confessions: One nun says she intentionally misbehaves because she enjoys being punished.

Like most super-fringe-y presentations, this one has a take-it-or-leave-it quality. I was glad to stream the first few hours from the comfort of home. But I'm also glad I didn't lose too much sleep over it.

The live performance of  "Abbot Adam: Matins/Lauds" — a copresentation by Philadelphia Contemporary and the Barnes Foundation — begins at 11:59 p.m. Saturday, following live-streamed installments Thursday and Friday night at www.barnesfoundation.org. Tickets are $8 to $16. Information 215-278-7000 or on the website.