Subah Sadiq

Sehri time expires at the time of Subah Sadiq. Subah Sadiq (Pre dawn) is when the time of Fajr enters. Sehri ends at the time of Subah Sadiq. As a precaution all eating must stop at least 5 minutes before the time of Subah Sadiq. 

Warning.

Many people continue to eat right to the time of Fajr Azaan. Fajr Azaan generally takes place approximately 5 to 10 minutes after Subah Sadiq. Thus a person having eaten up to this time would have eaten during the time of fasting. In such a case the fast will be invalid.

Courtesy: www.everymuslim.co.za