As far as the timings for prayers, there is a slight difference of opinion within the Sunni sects, and also between the Sunni and Shi'a point of view.
With the holy month of Ramadhan, and Iftar time, the Quran says to finish your fasting at "night time" (Surah al-Baqarah, verse, 187). Most Shi'ah jurists say this means it should be dark, including the fading of the redness in the eastern horizon.
The rational argument for this is that it is far better that one observes the basic level of precaution and wait until it gets 'dark', and becomes 'night'. Being patient for a few more minutes will guarantee the entering into the correct time of Layl.
However, Sunni scholars say with the setting of the sun one is able to break their fast, even if there is still redness in the horizon.
Shi'ah jurists also support their view by numerous traditions from Ahlul Bayt (a.s.) clearly mentioning this particular view.
And Allah knows best.