The 5 (five) daily prayers are obligatory (fard) and they are performed at times determined essentially by the position of the Sun in the sky. Hence, salah or prayer times vary at different locations on the Earth.
Fajr begins at subh saadiq — true dawn or the beginning of twilight, when the morning light appears across the full width of the sky — and ends at sunrise.
The time interval for offering the Zuhr or Dhuhr prayer starts after the sun passes its zenith and lasts until 20 min (approx) before the call for the Asr prayer is to be given. There is thus a long period of time within which this prayer can be offered, but people usually make their prayer within two hours after the Azan has been announced from Mosque.
The Asr prayer starts when the shadow of an object is the same length as the object itself (or, according to Hanafi fiqh , twice its length) plus the shadow length at zuhr, and lasts till sunset. Asr can be split into two sections; the preferred time is before the sun starts to turn orange, while the time of necessity is from when the sun turns orange until sunset.
The Maghrib prayer begins when the sun sets, and lasts till the red light has left the sky in the west. It usually lasts for about 18 to 20 minutes from the start of Maghrib Time.
The isha prayer starts when the red light is gone from the western sky, and lasts until the rise of the “white light” (fajr sadiq) in the east. The preferred time for Isha is at night or before midnight.