Qurtubi cites this narration and confirms that its chain of authorities is more authentic than the other tradition narrated by Sayyidna 'Imran Ibn Husain رضي الله عنه which talks about odd [three] and even [two/four] units of prayers. Therefore, Sayyidna Ibn 'Abbas رضي الله عنه 'Ikramah and Nahhas رحمهما الله تعالي have preferred the view that 'even' refers to the Day of Sacrifice and 'odd' refers to the day of 'Arafah.
Some commentators like Ibn Sirin, Masruq, Abu Salih and Qatadah رحمهما الله تعالي said that 'even' refers to the entire creation, because Allah has created them in pairs, and thus He says:
وَمِن كُلِّ شَيْءٍ خَلَقْنَا زَوْجَيْنِ
'And from everything We have created (apair of) two kinds [51:49]
belief/disbelief, happiness/unhappiness, light/darkness, night/day, cold/ heat, sky/earth, human/Jinn and male/female as against all of these pairs, Allah is the only One Being 'odd' that does not have a pair:
'He, is Allah, the One, Besought of all, needing none'
وَاللَّيْلِ إِذَا يَسْرِ (and by the night when it moves away...89:4). The word yasr is derived from sara and means 'to walk in the night' or 'travel by night'. The verse says when the night itself moves away. It signifies 'when the night departs and goes away.' After taking oath by these five items, the next verse says:
هَلْ فِي ذَٰلِكَ قَسَمٌ لِّذِي حِجْرٍ (Is there [not] in that an oath (enough) for a man of sense?...89:5). An intelligent person is, in a very special style, invited to think and reflect. The word hijr literally denotes 'to prevent'. The intellect has been called hijr because it prevents the person from doing which is unbecoming of him actions or statements. Are these oaths not sufficient for a man possessed of intellect, sound reasoning, understanding and religious discernment? This sentence is in the form of interrogation to awaken man from his slumber. The subject of oaths is implied, though not stated explicitly. The verse purports to say that when man considers into the Majesty of Allah and reflects on the greatness of objects of oaths, it would be confirmed and verified that everyone has to give account of his deeds, and reward and punishment in the Hereafter is sure. In this connection, reference is made to the destruction of three previous nations:  the nation of 'Ad;  the nation of Thamud; and  the nation of Fir'aun (the Pharaoh). 'Ad and Thamud are two nations whose genealogy link up with Iram. Thus Iram may refer to both, 'Ad as well as Thamud. Here however with 'Ad only the name Iram is linked for genealogical reasons:
أَلَمْ تَرَ كَيْفَ فَعَلَ رَبُّكَ بِعَادٍ إِرَمَ ذَاتِ الْعِمَادِ Have you not seen how your Lord dealt
with [the people] 'Ad of Iram, the men of tall pillars...(89:6-7). The word 'Iram' in verse  is, grammatically speaking, either 'atf bayan (syndetic explicative) or badal (complement). The purpose of the construction is to specify one of the two tribes of 'Ad. This statement specifies that it refers to 'Ad-ul-'ula (the early generation of 'Ad). A remnant from the former generation is referred to as 'Au-ul-'Ukhra, because they are linked with their great-grand father Iram more closely than 'Ad-ul-'Ukhra. Here the Qur'an refers to the first tribe as 'Ad Iram. In Surah An-Najm, they are described as: عَادًا الْأُولَىٰ (the earlier 'Ad,) [53:50]'
They are introduced here by the epithet: ذَاتِ الْعِمَادِ (the men of tall pillars)
The word 'imad' and "amud' means 'pillar'. The people of 'Ad are mentioned as the men of tall pillars because they were very tall in stature. They were a stronger and more powerful people than any other nations. The Qur'an describes them explicitly, thus:
لَمْ يُخْلَقْ مِثْلُهَا فِي الْبِلَادِ (the like of whom were never created in the lands...89:8) The Qur'an made it clear that this nation was the tallest and the strongest in their physical stature, but the Qur'an did not state the exact measurement of the people because it was unnecessary [for Qur'anic purposes]. Therefore, that detail has been left out. Israelite traditions, however, narrate such incredible reports about their stature, height and power that are difficult to believe. It is reported from Sayyidna Ibn 'Abbas & and Muqatil that they were six yards or eighteen feet [5.46]. tall. This too seems to be derived from Israelite reports. And Allah knows best!
Some commentators say that 'Iram' is the name of the 'paradise' which 'Ad's son Shaddad had built. The epithet 'possessor of tall pillars' [translated above as 'men of tall pillars'] is used for him. The [so-called paradise] was a lofty structure standing on tall pillars built with gold and silver and studded with jewels, gems and other precious stones, so that people may prefer an instant and ready at hand paradise instead of Paradise of the Hereafter. When this magnificent palace was ready for use, and Shaddad, together with the leaders of his kingdom, wanted to enter, Divine punishment overtook them. They, together with the palaces, were completely destroyed. [Qurtubi]. In this interpretation, the verse refers to a specific punishment which descended upon the paradise built by 'Ad's son Shaddad. In the first interpretation, which the majority of the commentators prefer, it refers to all the punishments that descended upon the nation of 'Ad.