“Whoever reads Surah Al-Kahf on Friday, light will shine for him between the two Fridays.”
Reported by al-Hakim and al-Bayhaqi; graded sahih by al-Albani (Sahih al-Jami' 6470).
“Whoever memorizes ten verses from the beginning of Surah Al-Kahf will be protected from the Dajjal.”
Sahih Muslim 809.
In the Islamic calendar a day begins at sunset, so many scholars explain that the Friday reading can be done from Maghrib on Thursday until Maghrib on Friday.
Hadith references are given so you can check them. For rulings and personal questions, please ask a qualified scholar.