Why must we be finished eating 90 minutes before dawn, when we can break fast 15 minutes past sunset? When it is still slightly light?
The answers are as follows:
1. It is not obligatory to start fasting 90 minutes before dawn. A person is allowed to eat and drink until right before dawn or the time of fajr. However, it is recommended to refrain from eating or drinking 10-15 minutes before the commencement of fajr as a precaution due to differing opinions on the exact time of fajr, and how it is determined, in the northern and southern parts of the world.
2. As for breaking of the fast, a person may do so when the redness in the eastern horizon of the sky disappears. By taking a look at the sky in the opposite direction of the sun, a person can tell that the time of maghrib prayers has set in once the redness in the sky disappears, and hence it becomes the time to break the fast. In general, this (i.e. disappearance of redness) normally occurs between 10-15 minutes after the time of sunset in the middle parts of the Earth (from the equator, both north and south until just above the subtropics), and specifically depending on the geographic location.