Starting the fast
I)Time of begining the fast
"and eat and drink until the whiteness of the day becomes distinct from the blackness of the night at dawn,then complete the fast till night"(2:187)
II)Time to stop eating
SAHIH BUKHARI,Volume 1, Book 10, Number 550:
Narrated Qatada:
Anas bin Malik said, "The Prophet and Zaid bin Thabit took the 'Suhur' together and after finishing the meal, the Prophet stood up and prayed (Fajr prayer)." I asked Anas, "How long was the interval between finishing their 'Suhur' and starting the prayer?" He replied, "The interval between the two was just sufficient to recite fifty 'Ayat." (Verses of the Quran)."