Is it permissible to use the word "when" to ask about an unseen matter?

There is no harm in asking about unseen matters using the word "when" (مَتَى), whether these are matters of the afterlife or future worldly affairs. People asked the Prophet, peace and blessings be upon him, about the time of the Hour, and he did not forbid them. He informed them that he did not know it and directed their attention to preparing for it. Similarly, the believers in the Quran asked: "When will the help of Allah come?" (متى نصر الله؟). There is also no harm in asking about the timing of unseen matters if the questioner believes that their timing has been mentioned in the Book or the Sunnah (definition), such as: When will the believers reach the Pond? When will the Dajjal emerge? And when will Gog and Magog emerge?