I have found that the optimum duration of a recital without intermission should be around 60 minutes (with stop changes). However, the ideal length of a recital depends on other factors, such as how cold it is in the room.
If the recital is during winter time and the church is not heated, it is probably better to make it shorter than usual, perhaps 30-45 minutes. Otherwise, people might catch cold during your playing. If the building is heated all year round, you can make the length of a recital as usual - around 60 minutes.
In cases when the program consists of long cycles, such as Clavierubung III, the Art of the Fugue, 18 Great Chorale preludes or other collections by Bach or other composers, you can plan for a longer duration. This is acceptable because people will expect it to be longer.
If the recital is with intermission, each part could last around 40-45 minutes (encores not including). This is usually the case in large concert halls.
The length of the recital does not matter so much in cases where the organist is of world class caliber. Then the listeners would not want him or her to stop playing anyway. In such cases, one or more encores is normal.
Generally speaking, it is better that listeners would want for more music than to become bored. In other words, if your program is just a little under 60 minutes (around 50-55 minutes) it is OK. There is no need to try to squeeze in an extra piece or two if the program is ideally balanced.
In addition, you have to remember that people who are going to attend your recital, might be frequent concert-goers and they might be used to the normal recital format of 60 minutes.
I usually plan around 50 minutes of pure music. That leaves me around 10 minutes for registration changes between the pieces.
One more thing is important to remember here. If you plan on talking during the recital, try to calculate the time of your presentations so that recital would not last too long.
The bottom line is this: your listener's time is as precious as yours - don't make your recitals too lengthy.
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