Should I maintain the time of the Ishā' prayer or congregational prayer if the Imām performs it before its correct time?

Prayer times are known by cosmic signs. The preferred time for Isha begins with the disappearance of the red twilight. The time interval between Maghrib and Isha varies. If the mosque congregation prays Isha after its legal time has begun, then be keen to pray with them due to the immense reward therein, knowing that congregational prayer in the mosque is obligatory for an able man. If the Imam is just and knowledgeable of prayer times, then follow him and pray with the congregation. However, if you ascertain that they are praying before the legal time has begun, then praying with them will not be sufficient for you, and you should pray at its correct time, even if alone in your home.