Say, "God is fully aware how long they remained, to Him is the unseen of heavens and earth, He sees and hears. They do not have besides Him any ally, nor does He share in His judgment with anyone."
Translation endnotes
[18:9-27] These 19 verses contain numerous key words that strongly imply that the story of the cave have double meaning like the verses in chapter 74, and the second meaning is about a prophetic event. I have already observed examples of a hidden mathematical design, and God the most Wise will unveil it when the right time comes. When the secrets contained in the cave is revealed by divine permission, it will prove once again the truth in the assertion at 18:27.