COMMENTARY on 17:78
Mustafa Khattab:

Translation:
Observe the prayer from the decline of the sun until the darkness of the night and the dawn prayer, for certainly the dawn prayer is witnessed ˹by angels˺.15
Commentary:
15   This verse gives the times of the five daily prayers: the decline of the sun refers to the afternoon and late afternoon prayers, the darkness of night refers to sunset and late evening prayers, then the dawn prayer.

 

A. Yusuf Ali:

Translation:
Establish regular prayers - 2275 at the sun´s decline till the darkness of the night, and the morning prayer and reading: for the prayer and reading in the morning carry their testimony. 2276
Commentary:

2275  The Commentators understand here the command for the five daily canonical prayers, viz.: the four from the declination of the sun from the zenith to the fullest darkness of the night, and the early morning prayers, Fajr, which is usually accompanied by a reading of the Holy Qur'an. The four afternoon prayers are: Zuhr, immediately after the sun begins to decline in the afternoon; 'Asr, in the late afternoon; Maghrib, immediately after sunset; and Isha, after the glow of sunset has disappeared and the full darkness of the night has set in. There is difference of opinion as to the meaning of particular words and phrases, but none as to the general effect of this passage. (Cf. n. 3521).

2276  The morning prayer is specially singled out for separate mention, because the morning is a "Holy hour" and special spiritual influences act on the soul awaking from the night's rest Special testimony is borne to the prayers of this hour by the angelic host.

 

Muhammad Asad:

Translation:
BE CONSTANT in [thy] prayer from the time when the sun has passed its zenith till the darkness of night, and [be ever mindful of its] recitation at dawn: 95 for, behold, the recitation [of prayer] at dawn is indeed witnessed [by all that is holy]. 96
Commentary:
95  As is evidenced by the practice (sunnah) of the Prophet, this verse fully circumscribes the five daily prayers laid down in Islam as obligatory for every adult man and woman: at dawn (fajr), shortly after the sun passes its zenith (zuhr), in the middle of the afternoon (`asr), immediately after sunset (maghrib), and after the night has fully set in (`isha'). Although parts of the Qur'an should be recited in every prayer, the early morning prayer is metonymically singled out as the "recitation (Qur'an) at dawn" because the Prophet, under divine inspiration, used to lengthen his recitation while praying at that time, thus stressing the special significance of this particular prayer. (See next note.)
96  Most of the classical commentators take this to mean "witnessed by the angels of night as well as those of day", since dawn is the time between night and day. Razi, however, is of the opinion that the "witness" to which the Qur'an refers here is the spark of God-given illumination in man's own soul-the heightening of his inner perception at the time when the darkness and stillness of night begins to give way to the life-giving light of day, so that prayer becomes a means of attaining to deeper insight into the realm of spiritual truths and, thus, of achieving communion with all that is holy.