Is it required for breaking the fast to adhere to the sunset or the Azan, especially given the time difference between them in some regions?

The beginning of breaking the fast is determined by verifying the sunset, based on the Prophet's (peace be upon him) saying: "When the night approaches from this side and the day departs from this side, and the sun has set, then the fasting person has broken his fast." It is prescribed to break the fast when the entire disk of the sun disappears in a place where nothing obstructs its view. If something obstructs its view, then the criterion is the approach of darkness from the east.