From Abu Sa’eed al-Khudri, who said: “Whoever reads Surah al-Kahf on the night of Jumu’ah, will have a light that will stretch between him and the Ancient House (the Ka’bah).”(Narrated by al-Daarimi, 3407. This hadeeth was classed as saheeh by Shaykh al-Albaani in Saheeh al-Jaami, 6471)

“Whoever reads Surah al-Kahf on the day of Jumu’ah, will have a light that will shine from him from one Friday to the next.”
(Narrated by al-Haakim, 2/399; al-Bayhaqi, 3/249. Ibn Hajar said in Takhreej al-Adhkaar that this is a hasan hadeeth, and he said, this is the strongest report that has been narrated concerning reading Surah al-Kahf. See: Fayd al-Qadeer, 6/198. It was classed as saheeh by Shaykh al-Albaani in Saheeh al-Jaami’, 6470)

It was narrated that Ibn ‘Umar (may Allah be pleased with him) said: “The Messenger of Allah (peace and blessings of Allaah be upon him) said: ‘Whoever reads Surah al-Kahf on the day of Jumu’ah, a light will shine for him from beneath his feet to the clouds of the sky, which will shine for him on the Day of Resurrection, and he will be forgiven (his sins) between the two Fridays.'”

Al-Mundhiri said, this was narrated by Abu Bakr ibn Mardawayh in his Tafseer, with an isnaad with which there was nothing wrong.
(al-Targheeb wa’l-Tarheeb, 1/298)

The surah may be read during the night or the day of Jumu’ah. The night of Jumu’ah starts from sunset on Thursday, and the day of Jumu’ah ends at sunset. Therefore the time for reading this surah extends from sunset on Thursday to sunset on Friday.

Al-Mannaawi said:
Al-Haafiz ibn Hajar said in his Amaali: “In some reports it says ‘the day of Jumu’ah’ and in some reports it says ‘the night of Jumu’ah’. They may be reconciled by saying that what is meant is the day which includes the night and vice versa.” (Fayd al-Qadeer, 6/199)

May Allah forgive all our sins.
Ameen

الله أعلم
Allah knows best!