What is the precise criterion for the time of prayer, and how does one know if he is in the desert?

Question : The questioner says: I ask and say, what is the precise criterion for the time of prayer? It is possible that a Muslim does not determine the time precisely, and we have heard that prayer is not permissible before its time, even by a moment. So when does a person know the time of prayer if he is in the desert? May Allah reward you with good.

Answer : The Messenger of Allah (peace and blessings be upon him) explained the times of the prayers, their beginning and their end. The time for the Fajr prayer is from the appearance of the second dawn, which is the horizontal whiteness on the horizon after which there is no darkness, until the sun rises. The time for the Zuhr prayer is from the sun’s zenith, meaning from its departure from the center of the sky, until the shadow of every object becomes equal to its length. The time for the 'Asr prayer is from that time, meaning from when the shadow of every object becomes equal to its length, until the sun turns yellow. The time extends in case of dire necessity until the sun sets. The time for the Maghrib prayer is from the setting of the sun until the disappearance of the red twilight.
The time for the 'Isha' prayer is from the disappearance of the red twilight until the middle of the night. This is how the Prophet (peace and blessings be upon him and his family) explained it.
It is known that these signs are hidden from many people, especially in our time when people have relied on clocks and written timetables. But whoever is in the open land and observes this, it becomes clear to him easily. Yes. Thank you, Honorable Shaykh, and may Allah bless you and your knowledge, and may He make it beneficial for the Muslims.