On a rainy Saturday evening in late September, 175 guests gathered at the American Museum of Natural History in New York City, focused on something other than the 21,000-pound model of a blue whale suspended over their heads.

They came, some with timepieces on both wrists, to attend RollieFest, an invitation-only event for watch collectors that seems to aim at being larger, but nonetheless more selective, than similar meet-ups that have been growing in popularity around the world over the past decade.

“This is sort of like the Super Bowl for watch nerds,” said Dr. Michael Zeff, an endodontist who flew in from his home in Reno, Nev.

It was, he said, “a really special event for like-minded people who love collecting watches and being able to get together and talk about esoteric stuff that we enjoy, but maybe not a lot of people understand.”

RollieFest’s name was inspired by a nickname for Rolex (it almost was called Rolliepalooza, said its founder, Geoffrey Hess), but attendees wore watches from a variety of brands. Dr. Zeff, for example, had on a red IWC Portugieser from 1943. And like other attendees — or RollieFesters, if you will — he instantly rattled off its reference number, 325, as part of the watch’s description.

The connections weren’t limited to the wrist though. In the breast pocket of Dr. Zeff’s suit was a deliberately chosen accessory: a wool and silk square patterned with the shape of watch bezels by the celebrated designer Gerald Genta, one of the pocket square collaborations between the British fashion brand Drake’s and the digital watch platform Hodinkee.

The gathering, the second time RollieFest had been held, revolved around two main events. There was the Sept. 23 dinner in the museum’s Irma and Paul Milstein Family Hall of Ocean Life, with that huge whale model; the menu included lemongrass chicken in a Sichuan pepper reduction; and there was a short, enthusiastic speech by Mr. Hess.

A seated brunch the following day was held at the Rainbow Room, a private event space on the 65th floor of 30 Rockefeller Plaza in Midtown where RollieFesters also displayed their timepieces so fellow guests could try them on, photograph them or just generally gawk. (A farewell cocktail party was held that night at a flashy Porsche dealership on 11th Avenue, but about a third of the RollieFesters didn’t attend, in part because it coincided with the start of Yom Kippur.)

“People were coming from far and wide to be here and at great expense,” Mr. Hess, 54, said, “so I wanted the experience to feel worthwhile.” He culled the invitees from a list of contacts and friends that he has developed both as a collector — he has about two dozen timepieces, including Rolex, Panerai and Hermès — and from working, since 2016, in the watch industry.

He said he used similar care in choosing the venues. “Since there were so many people from outside of New York, let alone outside of the country, I wanted it to be places that I knew couldn’t be replicated in their hometown.”

An Authentic Event

Each RollieFester paid $1,300, which included the events and bus transportation to the museum.

It was an increase from the $850 cost of the first event in 2019, but Mr. Hess said his goal wasn’t to make money (adding that he spent about $10,000 of his own money on the first RollieFest).

“This is a noncommercial event,” he said emphatically. “The beauty of it is its authenticity.”

Sotheby’s — where Mr. Hess became senior vice president and head of watches for the Americas in August — provided what he described as “very nominal financial support,” although Mr. Hess and Sotheby’s declined to be more specific. The auction house did have a subtle presence throughout the weekend, with its logo on the souvenir baseball caps and Leigh Safar, a Sotheby’s vice president and its global head of important watch collections, on the four-person panel discussion after the Sunday brunch.

Of the 175 attendees, 41 came from countries that included Japan, United Arab Emirates and the Netherlands. Dr. Zeff was one of the 74 people who came from U.S. states other than New York.

The mix included doctors, lawyers and watchmakers, as well as a television producer, an Indianapolis 500-winning racecar driver and the actor Fred Savage, best known for his childhood role on the television show “The Wonder Years.” (Mr. Savage was on the Sunday panel, extolling the virtues of watch collecting with all the exuberance that his TV character, Kevin Arnold, used to show for his Topps baseball cards.)

“One of the reasons why watch collecting is so exciting,” Mr. Hess said, is that “you’re meeting people you wouldn’t otherwise meet, but for that little piece of jewelry on your wrist.” (His own wrist displayed four watches, in rotation, during the event, including a limited edition 2002 white gold A. Lange & Söhne Lange 1.)

The age range also covered quite a span, from the Los Angeles-based dealer Linden Lazarus, who is 20 years old, to several collectors in their 60s.

But, just like many watch collectors’ events, two groups were noticeably underrepresented: people of color and women.

Asked about the invitation list, Mr. Hess said that “all walks of life were there: old, young, male, female, all different cultures.”

“The real focus is the crème de la crème of the collectors’ community and those that would really enjoy being there most,” he added.

There were, however, just 21 female RollieFesters, including several Sotheby’s executives — none of whom were really surprised by the situation. “I’m used to it,” said Zoe Abelson, a watch dealer based in New York, “so at this point it’s not something that stands out to me when I go to a watch event.”

‘Do You Think It’s Crazy?’

Mr. Hess is well known in the watch collectors’ community. In addition to his personal interest in horology, which includes the @manhattanrollie Instagram account he has had since 2014, he has worked at the watch reseller Analog:Shift and in the watch department of Phillips auction house in New York.

Over the past decade or so, he had traveled to quite a few collectors’ get-togethers (or GTGs, as horology fans often call them), in countries that included France, Britain and Australia. “I always wondered why this great hobby didn’t have a similar kind of gathering in the United States,” he said, deciding in early 2019 that he should do something about it.

“Geoff had come to me with this idea: ‘Do you think it’s crazy? Do you think people would do it?’” said Vincent Brasesco, a colleague at Sotheby’s who also worked with Mr. Hess at Analog:Shift and has helped out at both RollieFests. “I was like, ‘It’s a great idea. I think people would really, really love it.’”

(He wore several watches over the weekend, including a 1955 yellow gold Jaeger-LeCoultre Cornes de Vache chronograph and a midcentury gold Patek Philippe, Ref. 1578GM, one of a 20-piece limited edition. On his feet at the Rainbow Room were custom-made Stubbs & Wootton velvet slippers with the words “Speed” and “Master” embroidered in the same distinctive font as the Omega model of the same name.)

The first gathering had a similar format to the second, with 110 attendees and dinner in an airplane hangar at the Intrepid Sea, Air & Space Museum on New York’s Pier 86. Mr. Hess said he intended to hold a 2020 session, but the pandemic forced a postponement.

‘As Big As It Gets’

Watch collectors’ clubs have been thriving, with organizations like the New York-based RedBar Group growing from a small local gathering in 2007 to about 90 chapters worldwide today. There also are small, very exclusive meet-ups like Issued, in England, and Vintage Rolex Asylum, in Indonesia.

As for RollieFest, “this one, to me, is a special event,” said Kevin O’Dell, whose LinkedIn page lists his profession as “watch hunter.” “This is as big as it gets.”

Mr. O’Dell, who drove almost five hours from his home in Leesburg, Va., to attend, brought about 30 timepieces from his 100-piece collection to the Rainbow Room, fewer than the 65 pieces he had shared at the 2019 event.

“I really promised I would only bring 12,” he said, “but then I was in my safe yesterday gathering everything, and I had 12 Cartiers alone. I was like, ‘I can’t just bring Cartiers.’”

Like the other attendees, Mr. O’Dell (who ended up bringing timepieces by Audemars Piguet, Boucheron and others, along with those Cartiers) displayed his watches on one of the tables that had been arranged on the Rainbow Room’s wooden dance floor in a three-spoke pattern meant to resemble the hour, minute and second hands on a watch dial.

Extremely valuable timepieces were removed from all sorts of cases — watch rolls, original cardboard boxes, velvet pouches, a gray Goyard zipped envelope — and left on the tables without much oversight from their owners.

“Everybody in the room has the utmost respect and accountability for this collectible hobby,” said Sam Matlick, a private money manager in Manhattan who laid out an eclectic array of more than 60 watches, including vintage Rolexes from the ‘60s and ‘70s. “I trust everybody — that’s all there is to it.”

On the streets of New York, however, he is not quite as trusting. He had taken an Uber from his home on the Upper East Side, carrying the watches in what he described as “a completely unmarked black backpack that looks completely discreet, on purpose.”

As Mr. Matlick spoke, a couple of men in crisp black suits looked down on the gathering from the mezzanine level, part of a team of five security people brought in to supplement each venue’s protective staff. The regional security director from Sotheby’s New York office, Christopher Wendler, was supervising.

“The most important thing for this event was security,” Mr. Hess said. “It is of paramount importance and was the central driver for numerous decisions, including the locations.”

In the lobby of Rockefeller Plaza, for example, there was a large sign that read “RollieFest NYC 23 Real Estate Conference” near the escalator leading up to the elevator lobby for the Rainbow Room. “It’s a big decoy,” Mr. Hess said.

Some attendees had their own strategies. Dr. Jimmy Field, a surgeon from the Houston area, came to the museum dinner with six Breitling timepieces tucked in a black nylon holder about the size of a salad plate that he had slung over his shoulder.

“If we were walking across any significant distance,” he said, “I’d take my coat off and put it under my coat so nobody would see.”

Some RollieFesters declined to be photographed or interviewed. One who stood out at the Rainbow Room brunch was wearing a casual black ensemble of T-shirt and pants, accessorized with dark Anna Wintour-esque sunglasses (to combat the air-conditioning, she said).

She insisted on being identified just as Old Watch Lady, or Owl for short, the name known by her more than 36,000 Instagram followers, and how she always is named in watch-related coverage.

She won’t use her real name in public or say exactly how many watches she owns — beyond, as she put it, “a fair few” — “because people can look it up, people can Google you, people can find out where you live, people can follow your movements, people can follow your business, and that makes me feel very vulnerable.”

She had flown from London to attend RollieFest. And Mr. Hess said there was “absolutely no reason why we couldn’t do a RollieFest outside of America, or even just outside of New York.

“Watches are global. I always think of wristwatches in some way like a universal language.”