The audience response is different at each show we witness that December week, as if ticket holders are the actors’ frenemies: supportive or withholding at any given moment. The actors are keenly attuned to the divergent reactions, and they’ve heard plenty about what strikes some people as the interminable Act 1. While, for instance, the set is greeted with varying amounts of applause at the curtain rise at the Wednesday matinee and evening performances, the audience is silent Tuesday night. On that occasion, Morse’s reaction is a desultory shrug.

Over the next two days, the actors and technical crew members, falling into patterns that make a long run look like an endless looping of the movie “Groundhog Day,” will stop to relate the rigors of their particular track.

“Every one of us in this play is running a different sort of race,” Mays says. Those races include unique pitfalls. Sherie Rene Scott, preparing in an upstairs dressing room for her role as prostitute Mollie Malloy, reveals the nasty bruise she acquired courtesy of one of the piece’s most dangerous stunts: In despair,Mollie jumps out of a window in the pressroom, which means that, eight times a week, Scott must leap nine feet into a specially built, foam-padded chamber in the basement that’s not always as easy a landing as you might think.

John Magaro, sitting at the table of hair and makeup supervisor Jenna B. DeJesus, reveals the knee and elbow pads he wears under his jailhouse garb as nebbishy escaped convict Earl Williams. Nightly, he bursts through another window made of breakaway glass, imported from California. In her dressing room, meanwhile, Holland Taylor talks about overcoming her reticence to play the part of Hildy’s mother-in-law, Mrs. Grant, which she initially saw as too minor to bother O’Brien about during rehearsals.

“I’ve never had the experience,” she explains, “of being a cog in such a magnificent vehicle.”

Act 1 introduces us to the gaggle of reporters — played by Mays, Dylan Baker, David Pittu, Lewis J. Stadlen, Clarke Thorell, Christopher McDonald and Joey Slotnick — who are staying late in the pressroom to report on a sensational event: the dawn execution of Earl, whom Mollie insists is innocent of the murder of which he’s been convicted. The reporters mercilessly taunt Mollie, and on her exit from one scene, the sobbing Scott can be spied at a backstage mirror, wiping tears off her smeared face.

“Once the waterworks get going, it’s not easy to turn them off,” she explains later.

It’s all a long setup for the antics and complications to come, including the efforts of Lane’s Walter to stop Slattery’s Hildy from leaving his paper to move to New York and marry pretty, young Peggy Grant (Halley Feiffer).

The production’s physical detail is remarkable, down to the coating of dust applied to the window sills, the 1920s Chicago Cubs pennant on the wall, even the working vintage water cooler in the corner. (“We did have an issue when the spigot accidentally got left on,” Phillips says. “Actors were skating around the stage.”)