Praise be to Allaah.
The time for Salaat al-Fajr is from the break of dawn until the time the sun rises. Whenever you pray during this time, you have performed the prayer on time. Whoever deliberately delays it until the sun has risen has committed a major sin, and some scholars say that he is like one who does not pray it at all. We must beware of delaying prayers until after their time is over. The length of the period between dawn and sunrise is approximately one and a half hours, as is stated in the timetable. These timetables have become a means for people to know the times for the prayers to the hour and minute, and we should pay attention to that, because the prayers are the foundation of Islam. The Muslim must pray regularly and on time, as Allaah says (interpretation of the meaning):
“And those who strictly guard their (five compulsory congregational) Salawaat (prayers) (at their fixed stated hours)” [al-Mu’minoon 23:9]
“Guard strictly (five obligatory) As-Salawaat (the prayers) especially the middle Salaat (i.e. the best prayer - ‘Asr)” [al-Baqarah 2:238]
The “middle salaah” is Salaat al-‘Asr.
Sheikh Muhammed Salih Al-Munajjid