Times of prayer
Question

                The time for ‘Asr coincides with the
      time of a lecture at college. The professor is a Christian and does not allow us time to
      pray, so we pray when we come out of the lecture, when there is only one hour left until
      Maghrib.
Praise be to Allah.Praying it at the beginning of its time is
    preferable, but praying it at the time you mention is OK and is still within the right
    time. It is not permissible to delay it until the sun becomes yellow, because of the
    saheeh hadeeth narrated by ‘Abd-Allaah ibn ‘Amr ibn al-‘Aas (may Allaah be
    pleased with him) who said: the Prophet  (peace and blessings of Allaah be upon him)
    said: “When you pray Fajr, its time is until the first horn of the sun appears (i.e.,
    until it begins to appear over the horizon). When you pray Zuhr, its time is until
    ‘Asr comes. When you pray ‘Asr, its time is until the sun becomes yellow. When
    you pray Maghrib, its time is until the reddish glow disappears. When you pray
    ‘Isha’, its time is until midnight.” (Saheeh Muslim, 5/109; Fatawa
    al-Lajnah al-Daa’imah, 6/121)
    Al-‘Ala’ ibn ‘Abd al-Rahmaan said: we entered upon Anas ibn Maalik after
    Zuhr and he got up and prayed ‘Asr. When he had finished his prayer, we mentioned
    praying too fast, or he mentioned it. He said, “I heard the Messenger of Allaah 
    (peace and blessings of Allaah be upon him) say, ‘That is the prayer of the
    hypocrites, that is the prayer of the hypocrites, that is the prayer of the hypocrites.
    One of them will sit until the sun turns yellow, and is between the horns of the Shaytaan,
    or on the horns of the Shaytaan, then he will get up and peck out four (rak’ahs), in
    which he does not remember Allaah except a little.’” (Reported by Abu Dawood,
    350). And Allaah knows best.