Opera singers are a bit like baseball pitchers - they both have to rest for a couple of days after a performance. In the case of the baseball player it's the pitching arm and shoulder which are in need of recuperation, while the opera singer has a voice to take care of. Since professional baseball teams have a stable of pitchers to choose from, they can play a game every day1 using a different starting pitcher each time. They might have a 'star' pitcher like Sandy Koufax who fans flock to see, but the team can still play without him. Opera fans, however, will often be attending the performance purely to see the star tenor or soprano in the leading role when they go to see Rigoletto or La Traviata, especially when that tenor is someone like Luciano Pavarotti. A stand-in simply won't do.
The Difference Between Opera Companies and Theatre Companies
Since, therefore, an opera can only be performed for one night at a time, opera houses work in a very different way to most other theatres. When a theatre puts on a play, the production runs night after night and even though the cast members may come and go, the play itself can run for weeks, months or even (in the case of Agatha Christie's The Mousetrap) decades. An opera company isn't able to do this because the principal singers have to rest, and this means that in the course of a single week, three or four different operas might be staged.
As you can imagine, this involves changing the set every day - something which a theatre presenting the same play for months on end doesn't have to do. Opera sets can be simple or complicated, but they have to be designed in such a way that the stage crew can easily dismantle (or 'strike') the set and build another one in the course of a working day.
But what if there's a dress rehearsal?
Most opera-goers only visit an opera house in the evening when they come to see a performance, but much activity goes on during the daytime. The set from the previous night's performance will be struck and a different set built for the coming evening. However, rehearsals throw a big spanner into the works. Opera companies generally have off-site rehearsal spaces and rooms, but there will come a point where a full dress rehearsal is necessary for both the cast and the crew, at the opera house. These sometimes take place on one of the evenings when there is no scheduled performance, but they usually happen during the day.
There isn't enough time in a working day to strike one set, build another for the rehearsal, strike that one, and then build a third set for the evening show. This is where the night crew enters the equation.
How The Night Change-over Works
Let's imagine this sequence of events: Fidelio begins at 7.30pm and ends (or 'comes down' in theatre parlance) at 10.00pm. There will be a dress rehearsal of Madame Butterfly at 10.00am the following day, and a performance of The Magic Flute at 7.30 that evening.
At 11.00pm the night crew will clock in and strike the Fidelio set. This can take anywhere from one to three hours depending on the complexity of the scenery, how many props there are to be stored away, and whether any of the scenery has to be loaded onto a lorry to be kept elsewhere for a few days until needed again2. As soon as the stage is bare they can begin building the set for the morning's rehearsal of Madame Butterfly. They might not have to build the entire set, which will be finished by the day crew when they clock in at 8.00 or 9.00am.
The rehearsal will last two or three hours, after which the day crew can strike that set and build the set for The Magic Flute. An evening stage crew will come in at 5.00 or 6.00pm to actually work on the show.
There is usually no regular working 'day' for the night crew, who are often employed on a casual basis and only called in when there is work to be done. They might finish work after only an hour or two or they might have to work right through the night and put in a full eight-hour shift. It all depends on the complexity of the sets involved and what time the dress rehearsal takes place. If you don't know how many hours you're going to be working you don't know how much money you're going to earn, and since this can play havoc with your monthly budget, it's common in the UK for opera house stage crews to be unionised and to have an agreement with the opera company about hours3. The agreement might be that they get either a four-hour 'call' or an eight-hour call, meaning that they're guaranteed to be paid for either four or eight hours, regardless of how many hours they actually work. This means that if you're called in for eight hours but only work five, you can still be earning money when you're at home tucked up in bed.
Nice work if you can get it4.