The 800-pound gorilla in the room from the start of CinemaCon — shortened theatrical release windows — was quiet for three days as Hollywood studios went about their annual bonding ritual with exhibs, presenting upcoming slates and cheerleading for the theatrical moviegoing experience.

Then on Day Four, the gorilla roared.

The announcement of Home Premiere, the industry’s official brand for premium video-on-demand offerings set to launch this month, went off like a bomb at Caesars Palace. The response from theater owners, who say they were not consulted about the venture, was swift.

“It seems that the risks far outweigh the benefits,” AMC topper Gerry Lopez told Variety.

The mood among exhibitors palpably darkened after Thursday’s news. Many grumbled about the timing, though the information was not a complete surprise to some, who told Variety they were expecting an announcement Monday. And though none seemed concerned that Home Premiere would actually cut into their bottom line, the consensus was that studios are sliding down a slippery slope.

“NATO has repeatedly, publicly and privately, raised concerns and questions about the wisdom of shortening the theatrical release to address the studios’ difficulties in the home market,” said the National Assn. of Theater Owners in a statement.

At the Thursday slate presentation by Warner Bros. — a participant in Home Premiere — Todd Phillips, director of “The Hangover 2,” spoke out strongly against the shrinking theatrical window.

“I’m on your side on the video-on-demand issue,” Phillips told the packed Colosseum, eliciting cheers and hollers from the crowd. “If I had wanted to make movies for television, I would have been a TV director.” David Heyman, producer of the “Harry Potter” franchise, later told Variety that he agreed with Phillips.

Despite the dust-up, CinemaCon attendees kept up appearances Thursday, attending in force presentations by Lionsgate and Warner Bros. Lionsgate screened boxing pic “Warrior” in its entirety and debuted trailers for “The Devil’s Double” and “Abduction”; Warner Bros. wrapped up the four-day conference by featuring generous portions of “Green Lantern,” “The Hangover 2” and the final installment of the “Harry Potter” franchise.

And just like they had over the entire course of the confab, exhibs sent up defiant cheers whenever a speaker lauded the theatrical experience.

Not content with cheers alone, NATO’s statement also appeared to threaten the studios with possibly withholding playing time for trailers as well as promo space.

“Additionally, cinema owners devote millions of hours of screen time each year to trailers promoting the movies that will play on their screens. With those trailers now arguably promoting movies that will appear shortly in the home market to the detriment of theater admissions, we can expect theater owners to calculate just how much that valuable screen time is worth to their bottom lines and to the studios that have collapsed the release window. The same consideration will no doubt be given to the acres of wall and floor space devoted to posters and standees,” said NATO.

Until the VOD plan from Warner Bros., Sony, Universal and 20th Century Fox was reported Thursday ayem on Variety.com, the topic had been largely avoided. At a CinemaCon news conference on Tuesday, NATO prexy and chairman John Fithian, along with MPAA head former Sen. Christopher Dodd, purposely avoided the topic. “Our exec board met (on Monday) and discussed what’s most important to us, and that was partnerships,” Fithian said. “It’s not about having a food fight.”

Instead, the confab focused on digital conversion, the future of 3D and the customary renewed commitment to fighting piracy. The latter issue was where Chris Dodd, the former senator and newly minted MPAA chief, squarely focused his first speech in his new role, committing himself to a future of aggressive lobbying for better education and stronger legislation.

Bizzers don’t think the VOD plan ultimately will work, questioning audiences’ willingness to shell out fees in the $30 range. But more to the point, the premium platform is unlikely to prop up the declining homevid market, they say.

NATO took a shot at telling the studios what’s good for them, warning that the plan would compromise Hollywood’s revenue stream.

“They risk damaging theatrical revenues without actually delivering what the home consumer seems to want, which is flexibility, portability and a low price,” NATO’s statement said.

NATO ended its statement saying, “These studios have made their decision in what they no doubt perceive to be their best interests. Theater owners will do the same.”