Firstly, I would like to know when is it the most preferable time to read surah kahf?
Wa Alaikum Asa Salaam,
The best time to recite Sura Kahf is at the beginning of the day. That is, after fajr on a Friday. Besides this time, during the day until sunset is also good.
And Allah Knows Best.
Mufti Waseem Khan.