When do the angels descend ?

The Descent of the Angels and the Decree for Every Good during the Night of Al-Qadr

Allah says, ﴿تَنَزَّلُ الْمَلَـئِكَةُ وَالرُّوحُ فِيهَا بِإِذْنِ رَبِّهِم مِّن كُلِّ أَمْرٍ ﴾ (Therein descend the angels and the Ruh by their Lord's permission with every matter.) meaning, the angels descend in abundance during the Night of Al-Qadr due to its abundant blessings. The angels descend with the descending of blessings and mercy, just as they descend when the Qur'an is recited, they surround the circles of Dhikr (remembrance of Allah) and they lower their wings with true respect for the student of knowledge. In reference to Ar-Ruh, it is said that here it means the angel Jibril. Therefore, the wording of the Ayah is a method of adding the name of the distinct object (in this case Jibril) separate from the general group (in this case the angels). Concerning Allah's statement, ﴿مِّن كُلِّ أَمْرٍ﴾ (with every matter.) Mujahid said, "Peace concerning every matter.'' Sa`id bin Mansur said, `Isa bin Yunus told us that Al-A`mash narrated to them that Mujahid said concerning Allah's statement, ﴿سَلَـمٌ هِىَ﴾ (There is peace) "It is security in which Shaytan cannot do any evil or any harm.'' Qatadah and others have said, "The matters are determined during it, and the times of death and provisions are measured out (i.e., decided) during it.'' Allah says, ﴿فِيهَا يُفْرَقُ كُلُّ أَمْرٍ حَكِيمٍ ﴾ (Therein is decreed every matter of decree.) (44:4) Then Allah says, ﴿سَلَـمٌ هِىَ حَتَّى مَطْلَعِ الْفَجْرِ ﴾ (There is peace until the appearance of dawn.) Sa`id bin Mansur said, "Hushaym narrated to us on the authority of Abu Ishaq, who narrated that Ash-Sha`bi said concerning Allah's statement, ﴿تَنَزَّلُ الْمَلَـئِكَةُ وَالرُّوحُ فِيهَا بِإِذْنِ رَبِّهِم مِّن كُلِّ أَمْرٍ - سَلَـمٌ هِىَ حَتَّى مَطْلَعِ الْفَجْرِ ﴾ (With every matter, there is a peace until the appearance of dawn.) `The angels giving the greetings of peace during the Night of Al-Qadr to the people in the Masjids until the coming of Fajr (dawn).''' Qatadah and Ibn Zayd both said concerning Allah's statement, ﴿سَلَـمٌ هِىَ﴾ (There is peace.) "This means all of it is good and there is no evil in it until the coming of Fajr (dawn).''