Question:
The Rasool ﷺ said: Do not turn your houses into graves and it is established that voluntary prayers are better performed at home. I try to pray nafl at home. I pray the sunnah in the musjid. The (potentially ignorant) ‘imam’ wants to ‘make it easier’ for people to attend. If I pray my voluntary rakahs at home before coming to the Musjid, I miss part of the congregation. Is it not rewarding to pray at home then come to the musjid. What is the ruling and should the imam adjust the time? Furnish evidence not ideas.
Answer:
Assalamualaikum Respect Br:
First and foremost, your question is appreciated. This answer is directed to the specific situation you described and should not be generalized to every community or circumstance. The matter should be approached as a whole, with attention to the intent of the Shariah and the full guidance of the Sunnah before us. The Rasool ﷺ encouraged believers to pray voluntary prayers in their homes and said, “The best prayer of a person is in his house except the obligatory prayer.” This includes nafl and Sunnah! Sure, we make exceptions to this rule due to our modern situations of distance, timings, etc. These exceptions are not rules. Rasool ﷺ also said, “Do not turn your houses into graves,” which the scholars explain as encouragement to keep the home alive with worship and prayer.
At the same time, congregational prayer is not a matter to be treated lightly. Rasool ﷺ gave a severe warning regarding neglect of the jamaah, which shows the great importance of attending prayer in congregation. These narrations make it clear that the Shariah places great weight on answering the call and preserving the congregation, and they should not be set against each other.
Accordingly, a worshipper should not deliberately miss the beginning of the jamaah in order to perform a voluntary act, especially when that act is not among the emphasized rawatib. The two rakahs before Isha, or according to some four rakahs, are recommended and virtuous, but they are not so emphasized that one should sacrifice the opening of the congregational prayer for them. The phrase “for whoever wishes” shows that this prayer is meritorious, not obligatory.
To establish the virtue of this prayer, there are reports from the early scholars indicating its desirability. Imam al-Mawsili mentions a narration from Aishah رضي الله عنها that the Rasool ﷺ prayed four rakahs before Isha and four after it, then rested. Imam Muhammad ibn Nasr al-Marwazi also reports from Said ibn Jubayr that they regarded four rakahs before Isha as praiseworthy. These narrations confirm the value of the practice, but they do not require it to be performed at home in every case, nor do they justify placing it ahead of the congregational prayer when time is limited.
Accordingly, if praying at home would cause one to miss the beginning of the congregational prayer, then preserving the jamaah takes precedence. One may come early to the masjid and pray the four rakahs after the adhan, and the reward for doing so remains great. This is especially fitting when one is careful to protect the prayer’s time and the unity of the congregation. The sounder course is to arrive early, pray the Sunnah, attend the congregation from the start, and if one wishes, to pray voluntary prayers at home at another time.
The imam should also consider the welfare of the congregation. If a slight delay brings clear benefit and no hardship for most people, it is permissible. In some places and seasons, this may be more suitable. In other cases, especially when the prayer time is already late, the imam should weigh the matter carefully and choose what best serves the congregation. In public worship, the needs of the congregation should come before personal preference. 

Allah Certainly Knows Best.
P.s. Kindly have a Mufti break the above points down and correct our thinking, should you feel it is incorrect. We would love their full explanation in writing. Please also note, we are living in a country wherin people have to go to work, their schedules matter, etc. A good response takes all this into consideration.