What if the sunset Adhan on Ramadan had been performed before the real time by about 7 minutes, believing that was the proper time, and all the site residents broke the fast?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Whoever breaks the fast believing that the sun has set and then finds out that the sun is still there, there is no expiation for him. There is a disagreement among the scholars on whether or not one has to make up this day. However, the majority of scholars, including the four Imams, are of the view that one should make up for this day because the fasting person should be certain that the sun has set before breaking the fast. Allah orders us to fast until nightfall; Allah Says (what means): {…and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night), then complete your fast till the nightfall.} [Quran 2:187].

Other scholars are of the view that his fasting is valid and he does not have to make up for this day. Their evidence for this is the Hadeeth reported by Al-Bukhari from ‘Asma’ (daughter of Abu Bakr) that she said: “We broke our fast during the lifetime of the Prophet on a cloudy day and then the sun appeared”. She did not mention that they were ordered to make up for this day. Ibn Taymiyyah said in his letter ‘The Crux of Fasting’, that Hishaam Ibn ‘Urwa (the reporter of this Hadeeth) reported from his father (‘Urwa) that they were not ordered to make up for that day. But in our view, it is better to make up for that day in order to be on the safe side.

Allah knows best.