When is it permissible to say "Ameen" behind the Imam?

In the name of Allah, the Most Gracious, the Most Merciful.
Praise be to Allah, and may peace and blessings be upon the Messenger of Allah. As for what follows, this is one of the tapes from the "Al-Huda wa al-Nur" series of scholarly lessons and legal rulings by our Shaykh, Muhammad Nasir al-Din al-Albani (may Allah preserve him). We ask Allah to benefit everyone with it. And now, with tape number two hundred and one.
Answers to phone calls

The Shaykh : You will remember this statement of mine if you pay attention in any mosque where you pray a prayer with loud recitation, and notice that all the people are racing the Imam to say "Ameen." The Imam has barely finished saying "not the misguided" before the mosque is filled with the sound of "Ameen." Therefore, the followers must be patient until they hear the Imam begin saying "Ameen," and then they should say it, acting in accordance with his (peace and blessings be upon him) saying: This is a hadith agreed upon by al-Bukhari and Muslim.The Shaykh : And perhaps you have finished your questions, so I, in turn, bid you farewell with "Peace be upon you."