the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
What matters is that the Sun has fully set. People might prefer to wait for the adhân to be called in order to be extra certain that the Sun has set – and also to avoid having to stare at their watches.
However, if it is known for certain that the adhân is being called considerably late, then a person may certainly break his or her fast before hearing the adhân. It is recommended to hasten breaking our fast after the Sun has set.
`Umar relates that Allah’s Messenger (peace be upon him) said: “When the night comes from that direction and the daytime departs in that direction and the Sun sets, then the fasting person has broken his fast.” [Sahîh al-Bukhârî (1954) and Sahîh Muslim (1100)]
Al-Bukhârî asserts that `Abû Sa`îd al-Khudrî used to break his fast as soon as the Sun’s disk disappeared over the horizon.
However, if a person is at the mosque and knows that eating before the adhân is called will bring about discord or commotion in the community, then he or she should refrain from eating for the sake of avoiding discord (fitnah) among the Muslims. Avoiding discord is obligatory, while hastening to break the fast is merely recommended.
And Allah knows best.
Source: Islam Today