It should be known that Prayer has a certain time in which a Muslim should offer it. Allah says, “Worship at fixed hours hath been enjoined on the believers” (An-Nisa’: 103). Also, the Prophet (peace and blessings be upon him) warned against ignoring offering Prayers in their due times.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: “Fajr time starts with the first appearance of dawn. The preferred time to pray Fajr is soon after without much delay while it is still dark. This, according to the majority of imams and scholars, had been the consistent practice of the Prophet (peace and blessings be upon him), as we can readily infer from the authentic traditions.
If, however, you were to wake up late, then you should pray before sunrise. It does not matter whether it is clear outside or not. The Prophet (peace and blessings be upon him) said, “If anyone oversleeps and misses a Prayer, he should do it as soon as he wakes up or remembers it.”
As far as the permissible time limit for Fajr, it extends from first break of dawn until sunrise. If, however, you were to wake up at the time of sunrise, you should wait for half an hour until the sun has risen well. This is because of the clear prohibition in the hadith about praying at the time of sunrise.
As far as Maghrib prayer is concerned, one should pray it without delay. The time of Maghrib, unlike other Prayers, is considered rather limited. So the sooner we pray the better. If, one could not pray earlier, he is still considered within the acceptable limits, if he does it before the red rays of the sun disappear from the horizon. Once the red rays disappear, the time of `Isha’ begins.”