The practice of some people is to stop eating Suhoor 10-15 minutes earlier than the time of Fajr to observe Imsak. This is not correct because Allah has permitted the fasting person to eat and drink until dawn comes.
Shaykh Ibn ‘Uthaymeen (raheemullah) was asked about some timetables which give the time of imsak as being approximately one-quarter of an hour before Fajr. He said:
"This is a kind of bid’aah (innovation) which has no basis in the Sunnah. Rather the Sunnah is to do the opposite, because Allah says in His Holy Book (interpretation of the meaning)":
...and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night) [al-Baqarah 2:187]
And the Prophet (صلى الله عليه وسلم) said: “Bilal gives the azan at night, so eat and drink until you hear the azan of Ibn Umm Maktoom, for he does not give the azan until dawn comes.” This imsak which some of the people do is an addition to that which Allah has enjoined, so it is false. It is a kind of extremism in religion, and the Prophet (peace and blessings of Allah be upon him) said: “Those who go to extremes are doomed, those who go to extremes are doomed, those who go to extremes are doomed.” Narrated by Muslim, 2670
Al-Nawawi (may Allah have mercy on him) said: "This shows that it is permissible to eat, drink, have intercourse etc until dawn comes."
Al-Haafiz ibn Hajar said in Fath al-Baari (4/199): "One of the reprehensible innovations that have appeared in our times is giving the second azan approximately twenty minutes before Fajr in Ramadhan, and extinguishing the lamps which indicate that it is haram to eat and drink for those who want to fast. Those who introduced this innovation claim that they are erring on the side of caution with regard to an act of worship."
What is obligatory on all Muslims is that they hold on firmly to the Qur'an and Sunnah and follow it as closely as one can. This is a safeguard for us, so that we don't fall right or left but stay on the middle course. The Prophet (صلى الله عليه وسلم) described the religion of Islam that is a middle course between extreme and lenient. Remember these words of the Prophet
(صلى الله عليه وسلم): I leave behind me two things. You will never go astray if you hold fast to them: The Qur'an and my Sunnah.
O Allah! Render the thoughts and inclinations within my heart, to be Your fear and remembrance, and let my endeavour and desire be devoted to what You love and appreciate. Keep my feet firm on Thy Right Path so that I should not stagger, and guide me to the true Faith so that I should not go astray. Ameen!!!