I was listening to Turandot on Saturday afternoon, and the first interval was a half hour, because they actually have to assemble the Royal Palace at every performance and that takes time. Most sets are on wagons and can be moved easily, but this one is different. Zefferelli was very precise about it.
When I saw Barber of Seville in 1997, the section between acts three and four was exciting. There was no interval, and it rained onstage as the set turned one way.
Figaro and Almaviva went the other way with a ladder so the Count could climb into Rosina's window and elope with her. It was spectacular.
The Met always lists the running time on their website, so if an Opera should end at 11:35PM, except for the ovations, they usually do. This is so people can get home.
Also, there are bows in front of the curtain after each act, and the ensemble never gets to take a bow.
NYC Visitor and Broadway Fan