Question:
How long do I have to say amen after someone makes a bracha?
Answer:
Hello,
It is the amount of time it takes to say the three (four) words, "Shalom alecha Rebbi (umori)", which is about one second. If a person is in a crowd which is answering amen, he may say it as long as they are still answering amen.
Best wishes
Sources:
Orach Chaim 124-8, MishnaBerura 124-34.
