18° Fajr Timetable

Why are Ramadan timetables differing significantly on the end of Suhoor/ beginning of Fajr time?

From the well known opinions regarding Fajr, the most cautious approach is to follow a timetable that uses 18 degrees to establish the beginning of Fajr. It is not advisable to continue eating after 18 degrees Fajr comes in as it does jeopardise the validity of one’s fast. For a more detailed explanation, please read the article in the link below:

https://untotheone.com/articles/ramadan-and-fixed-true-dawn/