In summer, around May 20 to July 20, the twilight in the sky doesn't disappear or disappears very late, after midnight.
It was narrated from 'Abdullah ibn 'Amr ibn al-‘Aas (may Allah be pleased with him) that he said:
The Messenger of Allah (blessings and peace of Allah be upon him) said:
"The time for Maghrib is when the sun sets, so long as the twilight has not disappeared. The time for 'Isha' is so long as half of the night has not passed."
Narrated by Muslim, 612.
The question that people would ask is if the twilight doesn't disappear, when is Isha time?
A hafiz told me that some people say you don't pray Isha at all, but this is blasphemy. He used the following verse and other evidence to support that you don't miss out Isha:
"Guard strictly (five obligatory) As-Salawat (the prayers) especially the middle Salat (i.e., the best prayer – 'Asr)."
He said that if you don't pray Isha at all, then there will be no middle salah as the order will be: Fajr, Zuhr, Asr and Maghrib, and Asr is the most important out of all of them.
What we see in salah timetables are estimated time for Isha, but we do not know, precisely so that will not be reliable as in some countries, the twilight never disappears or disappears very late that which there is not enough time to pray Isha.
Also, it is makrooh to pray Isha after midnight.
Ramadan is in the summer. This is why Taraweeh is prayed quite late. Also, in these countries, Suhoor is quite early. An example the hafiz told me was that in Norway, Maghrib is at 12:10, and Suhoor is at 12:40, meaning there are only 30 minutes to pray, so the people pray Maghrib and pray Isha straight after.
The problem is that student, teachers, etc. would be strongly affected by this. They would have to pray Taraweeh and get back home around 12, and then they will have to wake up for Suhoor at 2, pray Fajr at around 3:20, then wake up for school at six etc.
This hafiz told me that you should join Maghrib and Isha together, providing that you sleep straight after as you can stay up and could have prayed Isha later.
This hadith supports it:
Ibn' Abbaas (may Allaah be pleased with him) who said: The Messenger of Allaah (peace and blessings of Allaah be upon him) joined Zuhr and 'Asr, and Maghrib and 'Isha,' in Madeenah when there was no fear and no rain. According to the hadeeth of Wakee,' he said: I said to Ibn' Abbaas: Why did he do that? He said: So that his ummah would not be subjected to hardship, i.e., so that they would not face any difficulty.
Question: Is joining Maghrib and Isha salah together every day for two months allowed?
I'm asking this question as this hadith below says:
The Prophet (peace and blessings of Allaah be upon him) said when asked which deed is most beloved to Allaah:
"Prayer offered on time."
And if you keep joining up the prayer, you won't get the best deed.
Also, this article says that Hanafis don't allow joining up prayers except in 2 cases, and I mainly follow Hanafi madhab. Still, the hafiz also supports Hanafi madhab, but he won't follow the rule for that.