Shia delay their timings to break the fast as they consider it as sunnah to break the fast till the stars appeared in the sky and oppose the Sunni who breaks the fast just after the sun sets (Maghrib) which is in accordance to the traditions/sunnah of Mohammad صلی اللہ علیہ وسلم.
Rasool صلی اللہ علیہ وسلم said
إِذَا أَقْبَلَ اللَّيْلُ مِنْ هَا هُنَا، وَأَدْبَرَ النَّهَارُ مِنْ هَا هُنَا، وَغَرَبَتِ الشَّمْسُ، فَقَدْ أَفْطَرَ الصَّائِمُ
When night falls from this side and the day vanishes from this side and the sun sets, then the fasting person should break his fast.
[Sahih Bukhari 1954, Sahih Muslim 1100]
There are numbers of reports and narrations in shia books which are in support of the Sunni practice of breaking the fast after sun sets, even consensus (Ijma) of the Shia Scholars which proves that Shias are opposing the Sunnah of Mohammad صلی اللہ علیہ وسلم and Ahle Bayt عليهم السلام.
Imam Jafar As Sadiq عليه السلام said
اذا غابت الشمس فقد دخل وقت المغرب.
When the sun sets, the time of Maghrib has entered.
[Amaali by Sadooq, page 68]
Saydna Ali رضیﷲ عنه said Maghrib prayer should be performed after breaking the fast.
أَمَّا بَعْدُ، فَصَلُّوا بَالنَّاسِ الظُّهْرَ حَتَّى تَفِيءَ الشَّمْسُ مِنْ مَرْبِضِ الْعَنْزِ وَصَلُّوا بِهِمُ الْعَصْرَ وَالشَّمْسُ بَيْضَاءُ حَيَّةٌ فِي عُضْوٍ مِنَ النَّهَارِ حِينَ يُسَارُ فِيهَا فَرْسَخَانِ. وَصَلُّوا بِهِمُ الْمَغْرِبَ حِينَ يُفْطِرُ الصَّائِمُ، وَيَدْفَعُ الْحَاجُّ إِلَي مِنًي. وَصَلُّوا بِهِمُ الْعِشَاءَ حِينَ يَتَوَارَى الشَّفَقُ إِلَى ثُلُثِ اللَّيْلِ. وَصَلُّوا بِهِمُ الْغَدَاةَ والرَّجُلُ يَعْرِفُ وَجْهَ صَاحِبِهِ. وَصَلُّوا بِهِمْ صَلاَةَ أَضْعَفِهِمْ ، وَلاَ تَكُونُوا فَتَّانِين.
“Lead the Zuhr prayer till the shadow of a wall becomes equal to the height of the wall and read the Asr prayer when the sun is still bright and enough time of the day is left for a person to cover a distance of six miles. "The Maghrib prayers should be performed when people break their fasts" and when Hajj pilgrims return from Arafat. And the time for Isha prayer is when the red glow of the even twilight disappears from the West, till one-third of the night is still left. The morning prayers are to be performed when there appears enough light of the dawn for a man to recognize the face of his companion.
[Nahjul Balagha Maktoob 52]
Grand Shia Ayatollah Hussain Tabatabai Al Barojardi narrated from the author of al Da'a'im that he said:
وروينا عن أهل البيت صلوات الله عليهم بإجماع فيما رويناه عنهم (2) أن دخول الليل الذي يحل فيه للصائم الفطر هو غياب الشمس في أفق المغرب بلا حائل دونها يسترها من جبل ولا حائط ولا ما أشبه ذلك، فإذا غاب القرص في أفق المغرب فقد دخل الليل وحل الفطر.
We narrated from Ahle Bayt عليهم السلام that there was consensus concerning that which we learned from the reports from them, that the onset of night which makes it permissible for the fasting person to break the fast is the disappearance of the sun beneath the western horizon without any barrier which would prevent seeing it such as a mountain or wall and the like. When the disk disappears beneath the horizon, then the night has begun and it is permissible to break the fast.
[Ja'ami Ahadith as Shiah, vol 10, page 353].
