For decades, the opening of San Francisco’s cultural and social season followed a fixed timeline, so regular you could set your watch by it.

On the Wednesday after Labor Day, the San Francisco Symphony would get first dibs on things with its gala opening, usually (though not always) featuring a superstar soloist such as cellistYo-Yo Ma, pianistYefim BronfmanorBonnie Raitt, the blues icon who defies all categories.

Then on Friday, the San Francisco Opera would present the first staged opera of its season, followed by a second opera on Saturday and Opera in the Park (cosponsored by the Chronicle) on Sunday afternoon.

All of that is gone now.

I say this without sorrow, though perhaps with a hint of misty-eyed nostalgia for a system that served so many of us so well for so long. For the most part, I think it’s exciting to see these two organizations — perhaps the ones on the cultural landscape most naturally susceptible to getting stuck in their ways — playing around with the formula.

Which is precisely the goal.

“We’re in a place now where we are trying to learn from our experiences and our experiments,” San Francisco Opera General Director Matthew Shilvock told me by phone. “We’re trying to be very responsive to what audiences are looking for at the moment, and that’s changing a lot.”

How different are this season’s openings from what came before? Plenty.

The Opera plans to be the first to raise a curtain on the season with a concert Friday, Sept. 8, conducted by Music DirectorEun Sun Kimand featuring the superstar husband-and-wife team of tenor Roberto Alagna and soprano Aleksandra Kurzak. Then the War Memorial Opera House will be dark until the following Tuesday, Sept. 12, when the season’s first opera, Verdi’s “Il Trovatore,” opens.

The Symphony, meanwhile, is going to bide its time until Sept. 22, when its gala opening centers on a concert led by Music DirectorEsa-Pekka Salonen, with repertoire ranging from the traditional (Gustav Mahler and Richard Strauss) to the contemporary (Swedish composer Anders Hillborg’s “Rap Notes”).

No single aspect of this is unprecedented. Because of various constraints over the years, including those wrought by the COVID-19 pandemic or scheduling conflicts, there have been instances when the Opera began its season early or the Symphony started late.

But 2023 is the first year thatallthe old scheduling landmarks (other than Opera in the Park, which retains its hold on Sunday afternoon) have been jettisoned at the same time. The result is a sense that long-standing assumptions — even over things as comparatively superficial as timetables — are being newly reexamined.

How big a jolt all of this will represent may depend on how deeply immersed you were in the old setup. For me, there was always an air of dramatic frenzy surrounding the rat-a-tat rhythm of the openings, a feeling of thrilling surfeit like the climax of a fireworks display.

A long-ago Datebook editor once dubbed the days following Labor Day “Hell Week,” and even though there was something grandiose (and a bit self-pitying) about it, the appellation stuck. There were a lot of performances to hear, a lot of swanky parties to report on and a lot of on-the-spot photography to be processed, all in a very short period of time. It was energizing and also wearying.

So spreading these events out over the course of September probably makes a certain amount of sense. At any rate, there haven’t been many complaints, not even from the traditionalist old guard for whom the opening galas are landmarks of the calendar.

“We’ve had much less pushback than you might expect,” said San Francisco Symphony Executive Director Matthew Spivey. “You know, we’ve been down this road before, when we eliminated the Wednesday night subscription series and had to shift all our Wednesday subscribers to Thursday night.

“We were very concerned about patron response, but we found that the vast majority of subscribers were open to the move.”

Aside from scheduling, there remains the perennial quandary of figuring out what type of programming is best suited for a gala opening, which has to cater to a heterogeneous audience that includes donors, regular subscribers and curious first-timers.

“Galas are notoriously difficult to program and to really get right,” Spivey said. “There is a traditional model where you have an iconic celebrity artist playing a concerto on the first half and then a big orchestral piece on the second half.

“That can work. There’s nothing wrong with that. But it’s not something that is easy to repeat.”

Since Salonen’s first season opener in 2021, the orchestra has been stretching those concepts year by year. Aprogram爵士贝斯手和歌手埃斯佩兰萨Spalding and Alonzo King Lines Ballet was followed last September by acollaborationwith the African-American Shakespeare Company. The upcoming performance of Hillborg’s “Rap Notes” features guest appearances by Oakland hip-hop artistKev Choice, freestyle artistAnthony Venezialeand Los Angeles soprano Hila Plitmann, a specialist in contemporary classical music.

At the Opera, meanwhile, replacing a fully staged show with a sleek, intermission-free concert feels like such an obvious move that it’s amazing it took this long to arrive.

The history of the company’s opening nights is littered with hilariously inappropriate choices for people who were either coming from or heading to a formal dinner — Verdi’s 4½-hour “Don Carlos,” for example, in 1986, or Virgil Thomson’s quirky, experimental “我们所有人的母亲” in 2003. A handful of arias and duets, and then off to the ball 90 minutes later, is a manifestly better scheme.

Still, there was one very concrete benefit to the old scheduling model, which was that the two companies could avoid stepping on one another’s feet like a pair of maladroit ballroom dancers.

This season, for the first time ever, the Opera will be opening a new production, the long-awaited local premiere of South Bay composer Mason Bates’ “The (R)evolution of Steve Jobs,” on the same night that the Symphony begins its season across Grove Street in Davies Symphony Hall. Anyone who had been hoping to attend both events (by which I mean, well, me) is going to be out of luck.

According to Spivey, this was simply a regrettable outcome of too many constraints operating at the same time.

“We have conversations with the Opera on a regular basis,” he said. “But sometimes conflicts like this come up, and you have to make a decision about what is the lesser of two evils.”

The important thing, after all, is that both companies can be free to alter the old traditions — even ones steeped in decades of habit — when they cease being responsive to the audience’s needs.

I’m not going to lie — I miss Hell Week, even in spite of that stupid name. It was dynamic and invigorating, a wonderful burst of music and spectacle. But I’ll survive.

It’s far more important for these companies and others like them to meet their patrons and future donors where they are. And if that means rethinking September from scratch, I’m there for it.

Reach Joshua Kosman:jkosman@sfchronicle.com;Twitter:@JoshuaKosman