Allah is informing about the approach of the Hour in the past tense ﴿in Arabic﴾ in order to confirm that it will undoubtedly come to pass. This is like the following Ayat, in which the verbs appear in the past tense in Arabic:

﴿اقْتَرَبَ لِلنَّاسِ حِسَـبُهُمْ وَهُمْ فِى غَفْلَةٍ مُّعْرِضُونَ ﴾

(Mankind's reckoning has drawn near them, while they turn away in heedlessness.)﴿21:1﴾

﴿اقْتَرَبَتِ السَّاعَةُ وَانشَقَّ الْقَمَرُ ﴾

(The Hour has drawn near, and the moon has been cleft.) ﴿54:1﴾

﴿فَلاَ تَسْتَعْجِلُوهُ﴾

(so do not seek to hasten it.) means, what was far is now near, so do not try to rush it. As Allah said,

﴿وَيَسْتَعْجِلُونَكَ بِالْعَذَابِ وَلَوْلاَ أَجَلٌ مُّسَمًّى لَّجَآءَهُمُ الْعَذَابُ وَلَيَأْتِيَنَّهُمْ بَغْتَةً وَهُمْ لاَ يَشْعُرُونَ - يَسْتَعْجِلُونَكَ بِالْعَذَابِ وَإِنَّ جَهَنَّمَ لَمُحِيطَةٌ بِالْكَـفِرِينَ ﴾

(And they ask you to hasten the torment (for them), and had it not been for a term appointed, the torment would certainly have come to them. And surely, it will come upon them suddenly while they are unaware! They ask you to hasten on the torment. And verily! Hell, of a surety, will encompass the disbelievers) (29:53-54). Ibn Abi Hatim reported from `Uqbah bin `Amir that the Messenger of Allah said:

«تَطْلُعُ عَلَيْكُمْ عِنْدَ السَّاعَةِ سَحَابَةٌ سَوْدَاءُ مِنَ الْمَغْرِبِ مِثْلَ التُّرْسِ، فَمَا تَزَالُ تَرْتَفِعُ فِي السَّمَاءِ ثُمَّ يُنَادِي مُنَادٍ فِيهَا: يَا أَيُّهَاالنَّاسُ فَيُقْبِلُ النَّاسُ بَعْضُهُمْ عَلَى بَعْضٍ: هَلْ سَمِعْتُمْ، فَمِنْهُمْ مَنْ يَقُولُ: نَعَمْ، وَمِنْهُمْ مَنْ يَشُكُّ، ثُمَّ يُنَادِي الثَّانِيَةَ: يَا أَيُّهَا النَّاسُ فَيَقُولُ النَّاسُ بَعْضُهُمْ لِبَعْضٍ: هَلْ سَمِعْتُمْ، فَيَقُولُونَ: نَعَمْ، ثُمَّ يُنَادِي الثَّالِثَةَ: يَا أَيُّهَا النَّاسُ أَتَى أَمْرُ اللهِ فَلَا تَسْتَعْجِلُوه»

(When the Hour approaches, a black cloud resembling a shield will emerge upon from the west. It will continue rising in the sky, then a voice will call out, `O mankind!' The people will say to one another, `Did you hear that' Some will say, `yes', but others will doubt it. Then a second call will come, `O mankind!' The people will say to one another, `Did you hear that' And they will say, `Yes.' Then a third call will come, `O mankind!' The Event ordained by Allah has indeed come, so do not seek to hasten it.') The Messenger of Allah said:

«فَوَ الَّذِي نَفْسِي بِيَدِهِ، إِنَّ الرَّجُلَيْنِ لَيَنْشُرَانِ الثَّوبَ فَمَا يَطْوِيَانِهِ أَبَدًا، وَإِنَّ الرَّجُلَ لَيَمُدَّنَّ حَوْضَهُ فَمَا يَسْقِي فِيهِ شَيْئًا أَبَدًا، وَإِنَّ الرَّجُلَ لَيَحْلُبُ نَاقَتَهُ فَمَا يَشْرِبُهُ أَبَدًا قَالَ وَيَشْتَغِلُ النَّاس»

(By the One in Whose Hand is my soul, two men will spread out a cloth, but will never refold it; a man will prepare his trough, but will never water his animals from it; and a man will milk his camel, but will never drink the milk.'' Then he said, "The people will be distracted.'') Then Allah tells us that He is free from their allegations of partners to their worship of idols, and making equals for Him. Glorified and exalted be He far above that. These are the people who deny the Hour, so He says:

﴿سُبْحَانَهُ وَتَعَالَى عَمَّا يُشْرِكُونَ﴾

(Glorified and Exalted be He above all that they associate as partners with Him. )

﴿يُنَزِّلُ الْمَلَـئِكَةَ بِالْرُّوحِ مِنْ أَمْرِهِ عَلَى مَن يَشَآءُ مِنْ عِبَادِهِ أَنْ أَنْذِرُواْ أَنَّهُ لاَ إِلَـهَ إِلاَ أَنَاْ فَاتَّقُونِ ﴾

(2. He sends down the angels with the Ruh (revelation) of His command to those servants of His whom He wills (saying): "Warn mankind that none has the right to be worshipped but I, so have Taqwa of Me.'')