The standard rule of thumb for films that appeal to a more mature audience is that it takes that crowd a few weeks to get around to catching up with a new movie aimed their way.

Thursday night “previews” have been a regular practice for some years now, but unless the title has “Downton” and “Abbey” in it, that tends to be something seasoned filmgoers forget or ignore.

“Social Media Buzz” on such titles is negligible. Once that AARP card arrives in the mail, online addiction/utility slacks off.

So a middling Thursday meant little to Sir Ken Branagh’s equisite and fun third turn at the detecting of Hercule Poirot, Belgian epicurean and mustachioed crime solver.

“A Haunting in Venice,” loosely adapted from a Christie story, limited to a few locations and one big set and thus far cheaper than “Murder on the Orient Express” and “Death on the Nile,” had a good Friday, adding to Thursday night for a $5-6 million+ “opening day,” and is headed to the top of the box office charts with a $14.5weekend, according to Deadline.com’s Friday and Sat. updates.

The franchise pre-dates Disney’s purchase of 20th Century (no longer Fox), and the smartest play, aside from continuing to give Mr. B. the reins, was keeping costs down. This one cost less than half of the other two (just $45 million, per best-guesses). It’ll end up in the black worldwide, no problem.

Limiting costs and effects (that digital Nile boat, etc) gave Branagh an excuse for directorial flourishes and getting the most out of a less well-known cast. And the clever Irishman brought in Tina Fey, just for fun, and there you go. It’s the best-reviewed Agatha Christie adaptation in ages.

This is shaping up as the second worst box office weekend of the year, but “Oppenheimer” just crossed the $900 million mark, worldwide. So there’s that.

The blasphemously bad “The Nun II” is still drawing over $14.7 million, its unreliable estimators are claiming, almost certainly from towns where the superior horror offering “Satanic Hispanics” isn’t playing.

The race for the top spot may change when the “actuals” come in Monday.

“Equalizer 3” will have cleared $73-75 million, all-in, by midnight Sunday. That one’s drawing Denzel fans of all ages, but also a somewhat older crowd. And it’s good, which helps. $7.2 million?

“My Big Fat Greek Wedding 3” is pretty exhausted as an idea, and it fell off 60% from its opening weekend, but is still in the top 5. It might not reach $30 million by the time it loses its screens, but $4.7 on a second weekend will do, if it manages to draw near that for a coupld more weekends.

“Barbie” will have cleared $625 million by midnight Sunday, and if it didn’t drive a stake through the heart of comic book movie mania, it sure as shooting told Warner Brothers its money is better spent elsewhere (look at what they’ve been doing with “Aquaman).