For each of the five obligatory Prayers, there is an appointed time fixed in relation to the sun’s position.
The time of the Fajr or morning Prayer begins with dawn and ends just before sunrise.
The time of the Zhuhr or midday Prayer, begins after the sun has crossed the zenith point and has begun to decline.
The time of the ‘Asr Prayer is when the sun has further advanced in decline and reaches a point nearly half way between the beginning of decline and sunset, which we may call late afternoon but not very late. It ends up quite some time before sunset, when the sunlight has paled. Although it is not entirely forbidden to say the ‘Asr Prayer that late in the day, it is most certainly preferred that it be offered before daylight has started fading out while the sun is still above the horizon by a good measure.
It is to be remembered that at the times of sunrise, sunset and when the sun is at its zenith, it is forbidden to offer Prayers. Also, when the ‘Asr Prayer has been performed, no optional Prayer should be offered between that time and the time of sunset. Similarly, between morning prayer and sunrise no optional prayer should be offered.
The time of Maghrib Prayer begins immediately after the sun has set. It lasts till dusk. But the word dusk is differently understood by the different schools of Jurists. The Wahhabis and similar sects with a rigid attitude insist that Maghrib Prayer should be offered almost immediately after sunset and that the time of dusk, according to them, ends when the redness of the sunset gives way to a dusky grey. Many other sects believe that dusk lasts still when there is some light left on the horizon after sunset. According to such schools, the allotted time for offering Maghrib Prayer, is almost as long as that allotted for performing morning Prayer which lasts from early dawn to sunrise.
All schools of jurisprudence agree that the time for the Ishaa Prayer begins when dusk has finally disappeared, giving way to the darkness of night. According to most, this period lasts till midnight but some even extend it beyond midnight till one retires for sleep. It is, however, very strongly advised and preferred that Prayers should be generally offered at the beginning of their respective times and should not be delayed until the time is about to run out.