Allah ﷻ has enjoined upon Muslims five prayers throughout the day and night and has specified the following times for them:
The Dawn Prayer (Salaat-ul-Fajr): It consists of two units (rak‛aat, singular: rak‛ah); it begins at daybreak, the time of day when light first appears, and lasts until sunrise.
The Afternoon Prayer (Salaat-udh-Dhuhr): It consists of four units; its time begins when the sun declines westward from the middle of the sky and ends when the shadow of an object becomes equal in length to the object itself plus the length of its shadow when the sun was at its zenith.
The Late Afternoon Prayer (Salaat-ul-‛Asr): It consists of four units; its time begins after the time of Dhuhr ends and ends with the setting of the sun. Hence, if the shadow of an object becomes equal to the length of that object plus its length when the sun was at its zenith, then the time of Dhuhr ends and the ‛Asr time begins. A Muslim must perform it before the sun loses some of its intensity and turns yellow.
The Sunset Prayer (Salaat-ul-Maghrib): It consists of three units; its time begins with sunset, that is, when the sun disappears below the horizon and finishes with the disappearance of the red glow (evening twilight) in the western horizon.
The Late Evening Prayer (Salaat-ul-‛Ishaa’): It consists of four units; its time begins when the twilight has completely faded away and lasts until midnight. It could be offered, however, a little before dawn, if need be, and the reason is acceptable in Islam.
A Muslim may use prayer timetables and does not have to find out if the prayer appointed time has become due by himself.