Delaying Isha Prayer in Ramadan
Question

The Imam in our mosque delays `Isha’ prayer for almost an hour in Ramadan. Is this permissible?
Praise be to Allah.The time for `Isha’ prayer lasts from when the red afterglow in the sky after sunset disappears until halfway through the night. 
It is preferable to delay `Isha’ prayer so long as that does not cause any hardship to the people, because Abu Hurayrah (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings of Allah be upon him) said: “Were it not that it would be too hard for my Ummah, I would have commanded them to delay `Isha’ until one-third of the night had passed, or one half.” (Narrated by At-Tirmidhi, 167)
This Hadith indicates that it is recommended to delay `Isha’ so long as that does not cause hardship to the members of the congregation. If it will cause hardship to them, then the prayer should be brought forward. 
`Aishah (may Allah be pleased with her) said: The Prophet (peace and blessings of Allah be upon him) stayed late one night until most of the night had gone and the people in the mosque had fallen asleep, then he went out and prayed. He said, “This would be its time, were it not that this would be difficult for my ummah.” (Narrated by Muslim, 638) 
Jabir (may Allah be pleased with him) said, when he mentioned the times when the Prophet (peace and blessings of Allah be upon him) prayed: “He sometimes delayed `Isha’, and sometimes brought it forward if he saw that they had gathered early. But if he saw that they were coming late, he would delay it.” (Narrated by Al-Bukhari, 1/141; Muslim, 646. See Ma`rifat Awqat Al-`Ibadat by Dr. Khalid Al-Mushayqih, 1/291) 
In some countries, the people are accustomed to delaying `Isha’ for half an hour or so after the time for it begins, so that people can break their fast at leisure and get ready to pray `Isha’ and Tarawih. 
There is nothing wrong with delaying `Isha’ prayer, on condition that the Imam does not delay the prayer so much that he causes hardship to the members of the congregation, as mentioned above. 
It is better to refer to the people who attend the mosque and reach an agreement with them on the time for the prayer, because they know best what suits them. 
For more details, please see the following answers: 39818 , 20712 , 67911 , and 171813 .
And Allah knows best.