وَٱلَّيْلِ إِذَا يَسْرِ

Allah swears in this surah by 5 things in order to allude to their immense benefit in the dunya and the akhira.

He swear by the Fajr (dawn) time because it is the time when light fills the sky and people fill the streets to begin seeking their daily sustenance. Some say that the verse refers specifically to the Fajr prayer because the angels themselves stand to watch us when we pray it. 

He swears by the 'ten nights,' which can either be:
- the first ten nights of  Dhul-Hijjah
- the last ten nights of Ramadan
- or the first ten nights of Muharram
Note that the و here is a conjunction (harf 'atf), not a letter to indicate a new oath; this is according to Sibawayh.

He swears by 'the even and the odd.' This refers to either
- the Eid of Sacrifice and the Day of Arafah (10th and 9th of Dhul-Hijjah)
- or the daily prayers with allusion to some being in even numbers and some in odd.

And then He swears by the night when it 'travels.' The night itself does not travel, but is a time during which people travel, especially when their destination is far. This is a type of figurative language to describe something by one of its core features. This also alludes to the journey of the souls at night while we sleep. Notice in the Arabic how there is a letter missing (orig. 'yasree') and this was done in order to maintain the pattern of the ayahs.
(Taken from Safwat al-Bayaan li-Ma'aani al-Quraan by sh. Hasanayn Muhammad Makhloof with additional notes by sh. Ahmad Fadel)

#TafsirTools - Oaths in the Quran
There are three parts to an oath: 1. the verb (fi'l al-qasam) | 2. The subject of the oath (al-muqsam bihi) | 3. The object of the oath (al-muqsam 'alayhi)
1. The verb - simply the verb indicating that an oath is bing sworn. This is often omitted in the Quran, and its place is taken by a single letter (either a waw, baa', or taa'). So while the original expression would be 'I swear by the dawn' (uqsimu bil-fajri), here the waw takes the place  of both the verb and the preposition after it (uqsimu bi-). This is indicated by the jarr status of the subject of the oath. 
2. The subject of the oath - What is He swearing by? Here is is the dawn (al-fajr). While we can only swear by Allah, Allah swears by the great signs of His creation to allude to their greatness and to captivate our minds. 
3. The object of the oath- What is He swearing over/what is the main point of the oath? This usually follows the subject (or string of subjects) but is omitted here. We can estimate that God is swearing by the above that 'those who disbelieve in God and reject the resurrection will be punished.' 

See example in Surah al-Haqqah for an oath with no omissions. The verb :'I swear by' (uqsimu bi-), and the object of the oath: 'Indeed this is...' (...انه لقول)
(Taken from Safwat al-Bayaan li-Ma'aani al-Quraan by sh. Hasanayn Muhammad Makhloof with additional notes by sh. Ahmad Fadel)

Makes sense, idk why I even asked that question lol. Thank you for replying so fast 

Tafakari: Al-Fajr 89:4