They ask you about the Hour -- when will be its appointed time?
What do you have to mention of it.
To your Lord it is limited.
meaning, its knowledge is not with you, nor with any creature. Rather the knowledge of it is with Allah. He is the One Who knows the exact time of its occurrence.
ثَقُلَتْ فِى السَّمَـوَتِ وَالاٌّرْضِ لَا تَأْتِيكُمْ إِلاَّ بَغْتَةً يَسْـَلُونَكَ كَأَنَّكَ حَفِىٌّ عَنْهَا قُلْ إِنَّمَا عِلْمُهَا عِندَ اللَّهِ
Heavy is its burden through the heavens and the earth. It shall not come upon you except all of a sudden.
They ask you as if you have a good knowledge of it.
Say;
"The knowledge thereof is with Allah." (7;187)
Allah says here,
إِلَى رَبِّكَ مُنتَهَـهَأ
To your Lord it is limited. Thus, when Jibril asked the Messenger of Allah about the time of the last Hour he said,
مَا الْمَسْوُولُ عَنْهَا بِأَعْلَمَ مِنَ السَّايِل
The one questioned about it knows no more than the questioner.
Allah said,
إِنَّمَا أَنتَ مُنذِرُ مَن يَخْشَاهَا