ووقتُ الصومِ: من حينِ طلوعِ الفجرِ الثاني إلى غروبِ الشمسِ.
Translation: The fasting period runs from the appearance of true dawn until sunset.
The “second dawn” is the true dawn (al-fajr al-ṣādiq), the horizontally spreading light that marks the start of the Fajr prayer time. The fast runs from that instant until actual sunset.
Food and drink must cease at true dawn, not sunrise. Likewise, the fast does not end merely because the sky has become dim; the legally relevant end is sunset.