It is in principle true and explicitly clear from Quran that only Allah knows the exact time of Qiyamah and it is one of those unseen informations about the future, whose knowledge has not been shared with any other creation of Allah. But the question is has Allah chosen not to share any signs at all? the answer to this is no, Allah has given us signs about Qiyamah in Quran. The rise of Gog Magog being one of the major signs which changed the whole history of the world, was prophesized in Quran and gradually we are moving towards that condition where they would be charging from every valley and collide like waves of water and Qiyamah will emerge from that chaos [See: Quran 21:95-97 (Discussion 66721 • Reply 66739) AND Quran18:98-99].
Regarding the verses which apparently give an impression that it might happen in their lifetimes (i.e. the direct addressees) or that the day is near (e.g. Quran 33:63), there are two aspects to understand such statements:
i) The literary aspect:
Firstly, used as a way to direct attention of the those addressees (who were apparently mocking this claim of Qiyamah and demanding for it to be broght to them right away) towards the fact that had it come now, would you people be ready to face it? what if the day is near? what would you have gained by expending your energies in asking the wrong questions and mocking the prophet of Islam, if it were to come now, you people would be the biggest losers. All these terms can be used to describe the essence of those verses. They are actually not claiming that Qiyamah is near, infact they are making another claim that only Allah knows the exact time of Qiyamah, so why are you people (i.e. the direct addressees) wasting your time in asking the wrong questions instead of getting ready for his day as if it were near. Had you people known the reality of this world, you people would have claimed the same.
Secondly, it is also a human nature that when we look in the past, we tend to believe that all past was just a matter of yesteday, hence all the promises, expectations, fears and regrets that seemed to spread over a vast lifetime of 60-70 years, ultimately confine into a matter of days when seen in the hindsight. Therefore, the rejectors of message will also say on the day of judgement that life of this world was just a few days when they see it in the hindsight on the day of judgement, hence the promsie of Allah that it may be near will eventually seem true to everyone of the rejectors of the message. (See: Quran 23:112-115 AND Quran 20:103-104).
ii) The factual aspect: The term near is relative w.r.t each person and especially w.r.t Allah. Quran 22:47 tells us that one day for the Lord is equal to our thousand years. Therefore, in this context, the Qiyamah might just be a matter of days when seen from the perspective of Allah.