What Are the Times of the Five Daily Prayers?
Question

What are the times of the five daily prayers? What is the wisdom behind the allocation of these times for prayer? What is the time of necessity (waqt ad-darurah)? How can we work out when half of the night has passed?
Praise be to Allah.Allah has enjoined upon His slaves five prayers throughout the day and night at specific times decreed by the wisdom of Allah so that the slave may be in contact with his Lord in these prayers throughout all of these times. They are for the heart like water for a tree, given to it time after time, not all in one go and then it stops. 

Part of the wisdom behind doing the prayers at these times is so that people will not get bored or find it too difficult, which would happen if they all had to be done at once. Blessed be Allah, the Wisest of judges. ((From the Introduction to Risaalat Ahkaam Mawaaqeet al-Salaah (Essay on the Rulings on the Times of the Prayers) by Shaykh Muhammad ibn ‘Uthaymeen, may Allah have mercy on him). 
Times of the five daily prayers 
The times of the prayers were mentioned by the Prophet (peace and blessings of Allah be upon him) in the hadith: “The time for Zhuhr is from when the sun has passed its zenith and a man’s shadow is equal in length to his height, until the time for ‘Asr comes. The time for ‘Asr lasts until the sun turns yellow. The time for Maghrib lasts until the twilight has faded. The time for ‘Isha’ lasts until midnight. The time for Subh (Fajr) prayer lasts from the beginning of the pre-dawn so long as the sun has not yet started to rise. When the sun starts to rise then stop praying, for it rises between the two horns of the Shaytan.” (Narrated by Muslim, 612). 
This hadith explains the timings of the five daily prayers. As for defining them by the clock, that varies from one city or country to another. We will define each in more detail as follows: 
1 – The time of Zhuhr 
The Prophet (peace and blessings of Allah be upon him) said: “The time for Zhuhr is from when the sun has passed its zenith and a man’s shadow is equal in length to his height (this is the end time), until the time for ‘Asr comes.” So the Prophet (peace and blessings of Allah be upon him) defined the start and the end of the time for Zhuhr: 
The start of the time for Zhuhr is when the sun has passed its zenith i.e., has passed the highest part of the sky and started to descend towards the west. 
Practical way of knowing when the zenith has been passed (and the time for Zhuhr has begun): 
Put a stick or pole in an open place. When the sun rises in the east, the shadow of this stick will fall towards the west. The higher the sun rises, the shorter the shadow will become. So long as it keeps growing shorter, the sun has not yet reached its zenith. The shadow will keep on growing shorter until it reaches a certain point, then it will start to increase, falling towards the east. When it increases by even a small amount, then the sun has passed its zenith. At that point the time for Zhuhr has begun. 
Knowing the time of the zenith by the clock: divide the time between sunrise and sunset in half, and that is the time of the zenith. If we assume that the sun rises at 6 a.m. and sets at 6 p.m., then the zenith is at 12 noon. If it rises at 7 a.m. and sets at 7 p.m., then the zenith is at 1 p.m., and so on. See al-Sharh al-Mumti’, 2/96 
The end of the time for Zhuhr is when the shadow of everything is equal in length to the object itself, plus the length of the shadow of the object at the time of the zenith.  
Practical way of knowing when the time for Zhuhr has ended
Go back to the stick or pole which we described above. Let us assume that its length is one meter. We will notice that before the sun reached its zenith, the shadow decreased gradually until it reached a certain point (make a mark at this point), then it started to increase, at which point the time for Zuhr began. The shadow will continue to increase, falling towards the east until the length of the shadow is equal to the length of the object itself, i.e., it will be one meter long, starting from the point marked at the zenith). As for the shadow before the mark, that is not counted, and it is called fay’ al-zawaal (the shadow of the zenith). At this point the time for Zuhr ends and the time for ‘Asr begins straight away. 
2 – The time of ‘Asr 
The Prophet (peace and blessings of Allah be upon him) said: “The time for ‘Asr lasts until the sun turns yellow.” 
We know that the time for ‘Asr begins when the time for Zhuhr ends, i.e., when the length of an object’s shadow becomes equal to the length of the object itself. There are two times for the end of ‘Asr. 

The preferred time: this lasts from the beginning of the time for ‘Asr until the sun begins to turn yellow, because the Prophet (peace and blessings of Allah be upon him) said: “The time for ‘Asr lasts until the sun turns yellow.” Defining this time by the clock varies according to the season.
The time of necessity. This lasts from the time the sun turns yellow until sunset, because the Prophet (peace and blessings of Allah be upon him) said: “Whoever catches up with one rak’ah of ‘Asr before the sun sets has caught up with ‘Asr.” (Narrated by al-Bukhari, 579; Muslim, 608) 

What is meant by the time of necessity? 
Necessity here refers to when a person is distracted from praying ‘Asr by some essential and unavoidable work, such as dressing wounds, and he is able to pray before the sun turns yellow but it is difficult, then he prays just before sunset. In this case he has prayed on time and has not sinned, because this is the time of necessity. If a person is forced to delay the prayer, there is no sin so long as he prays before the sun sets. 
3 – The time of Maghrib 
The Prophet (peace and blessings of Allah be upon him) said: “The time for Maghrib lasts until the twilight has faded”, i.e., the time for Maghrib starts immediately after the time for ‘Asr ends, which is when the sun sets, until the twilight or red afterglow has faded. When the red afterglow has disappeared from the sky, the time for Maghrib ends and the time for ‘Isha’ begins. Defining this time by the clock varies according to the season. When you see that the red afterglow has disappeared from the horizon, this is a sign that the time for Maghrib has ended. 
4 – The time of ‘Isha 
The Prophet (peace and blessings of Allah be upon him) said: “The time for ‘Isha’ lasts until midnight.”  
So the time for ‘Isha’ begins immediately after the time for Maghrib ends (i.e., when the red afterglow disappears from the sky) until midnight. 
How do we calculate when midnight is? 
If you want to calculate when midnight is, then calculate the time between sunset and the break of true dawn (when Fajr begins) then divide it in half; that halfway point is the end of the time for praying ‘Isha’ (and that is midnight). 
So if the sun sets at 5 p.m., and Fajr begins at 5 a.m., then midnight is 11 p.m. If the sun sets at 5 p.m. and Fajr begins at 6 a.m., then midnight is 11.30 p.m., and so on. 
5 – The time of Fajr 
The Prophet (peace and blessings of Allah be upon him) said: “The time for Subh (Fajr) prayer lasts from the beginning of the pre-dawn so long as the sun has not yet started to rise. When the sun starts to rise then stop praying, for it rises between the two horns of the Shaytan.” 
The time for Fajr begins with the onset of the “second dawn” (al-fajr al-thani) and ends when the sun starts to rise. The “second dawn” is the brightness that appears along the horizon in the east and extends north to south. The “first dawn” (al-fajr al-awwal) occurs approximately one hour before this, and there are differences between the two: 

In the “first dawn” the brightness extends from east to west, and in the “second dawn” it extends from north to south.
The “first dawn” is followed by darkness, i.e., the brightness lasts for a short period then it becomes dark. The “second dawn” is not followed by darkness, rather the light increases.
The “second dawn” is connected to the horizon, with no darkness between it and the horizon, whereas the “first dawn” is separated from the horizon with darkness between it and the horizon. See al-Sharh al-Mumti’, 2/107.

For more information, see answers No. (1092 ) and (48998 ).
And Allah knows best.