It's funny how truisms come to pass in Las Vegas entertainment.

There are entire Web sites tracing the origin of urban legends, like the one about the guy who wakes up in the hotel room without his kidney.

I've got one that isn't nearly as salacious, but just as worthy of study: Las Vegas showgoers won't sit through anything longer than 90 minutes.

It's a fairly young notion, and, I would argue, not a completely tested one. But in just a few years, it has almost irreversibly crossed from theory to accepted fact.

Most recently, it was restated by the great Mel Brooks. "Las Vegas is not particularly attuned, attention-wise, to listening to the plot, to listening to the intricacies of the story. It's a tough town for a book show," he noted, talking up "The Producers" at Paris Las Vegas. "I think without bragging -- or with bragging -- we're the only book show that can make it here."

That's not likely to sit well with locals, who don't consider themselves simple and may even resent paying top dollar for a ruthlessly chopped production. They're more likely to cite another explanation, voiced at the same press event by the show's featured star, David Hasselhoff: "It rocks from beginning to end," he said of the abbreviated musical, "and everybody can still go out and get on the tables."

So here are two accepted notions. To presenters, audiences are restless, ready to move on. They cite patrons bolting during intermissions for "Avenue Q" at Wynn Las Vegas and "Chicago" at Mandalay Bay.

To consumers, it's an old casino custom going back to the days of entertainment as a loss leader. Every minute over 90 (really, more like 75 in the old days) had a direct impact on the casino drop.

The truth isn't so simple. Nowadays, it helps to know the "casino contract" for Actors Equity Union allows producers to do 10 shows at 90 minutes for the same price as eight longer ones each week.

It also can be a case-by-case issue of how a show plays. "The Producers" didn't cut down so well, but surprisingly, "The Phantom of the Opera" did. One show tested a compromise idea I support: Cut the intermission, but let the time run anywhere from 100 to 110 minutes.

Unfortunately, that show was "We Will Rock You" and it wasn't very good. Cutting it to 90 minutes as a last-ditch effort kind of improved it. I would rather have seen the superior "Hairspray" test the added breathing room of, say, 10 extra minutes.

One guy at least did his own research. Eric Idle says that before making the call on "Monty Python's Spamalot," he "came and watched the shows and went through a week here of seeing everything" before deciding on 90. "That's what the Vegas length is."

For his show, he's probably right. Other producers should perhaps not be so quick to accept theory as fact.

Mike Weatherford's enterainment column appears Sundays and Thursdays. Contact him at mweatherford@reviewjournal.com or 383-0288.