As far as Islamic Shari`ah is concerned, breaking the fast should be done at sunset which is the time of Maghrib Prayer. To delay breaking the fast after sunset until it gets dark is rigidity and violation to the Prophet’s sunnah.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: Shari`ah has provided simple, physical signs for beginning and ending of Ramadan. One is required to abstain from food, drink, and gratifications from dawn to dusk. More precisely, one does so from the time of Fajr Prayer to time of Maghrib. There is no need to wait for darkness to set in. In other words, as soon as sun has set, one should break the fast. This is the well-established sunnah of the Prophet (peace and blessings be upon him). To delay it until it gets dark is rigidity and amounts to a clear violation of the Prophet’s Sunnah. The Prophet (peace and blessings be upon him) said, “My Ummah will continue to be blessed by Allah as long as they delay their predawn meal and as long as they hasten to break their fasts as soon as the sun has set!”
The Prophet (peace and blessings be upon him) has also warned against rigidity in religion, “This religion of ours is rather simple and easy; whoever makes it rigid will only destroy himself.” He also said, “Woe to those who practice rigidity in religion.” He repeated these words thrice.