فَيَأْتِيَهُم بَغْتَةً ...

It shall come to them of a sudden,

means, the punishment of Allah will come upon them suddenly,

... وَهُمْ لَا يَشْعُرُونَ ﴿٢٠٢﴾

فَيَقُولُوا هَلْ نَحْنُ مُنظَرُونَ ﴿٢٠٣﴾

while they perceive it not. Then they will say: "Can we be respited!''

means, when they see the punishment, then they will wish they had a little more time so that they can obey Allah -- or so they claim.

This is like the Ayah:

وَأَنذِرِ النَّاسَ يَوْمَ يَأْتِيهِمُ الْعَذَابُ فَيَقُولُ الَّذِينَ ظَلَمُواْ رَبَّنَا أَخِّرْنَا إِلَى أَجَلٍ قَرِيبٍ نُّجِبْ دَعْوَتَكَ وَنَتَّبِعِ الرُّسُلَ أَوَلَمْ تَكُونُواْ أَقْسَمْتُم مِّن قَبْلُ مَا لَكُم مِّن زَوَالٍ

And warn mankind of the Day when the torment will come unto them; then the wrongdoers will say: "Our Lord! Respite us for a little while, we will answer Your call and follow the Messengers!'' (It will be said:) "Had you not sworn aforetime that you would not leave (the world for the Hereafter).'' (14: 44)

When every sinner and evildoer sees his punishment, he will feel intense regret. Such was the case of Fir`awn, when Musa prayed against him:

رَبَّنَا إِنَّكَ آتَيْتَ فِرْعَوْنَ وَمَلأهُ زِينَةً وَأَمْوَالاً فِي الْحَيَاةِ الدُّنْيَا رَبَّنَا لِيُضِلُّواْ عَن سَبِيلِكَ رَبَّنَا اطْمِسْ عَلَى أَمْوَالِهِمْ وَاشْدُدْ عَلَى قُلُوبِهِمْ فَلاَ يُؤْمِنُواْ حَتَّى يَرَوُاْ الْعَذَابَ الأَلِيمَ

قَالَ قَدْ أُجِيبَت دَّعْوَتُكُمَا

Our Lord! You have indeed bestowed on Fir`awn and his chiefs splendor and wealth in the life of this world, our Lord! That they may lead men astray from Your path. Our Lord! Destroy their wealth, and harden their hearts, so that they will not believe until they see the painful torment.'

Allah said: "Verily, the invocation of you both is accepted. (10:88-89)

This supplication had an effect on Fir`awn: he did not believe until he saw the painful torment:

حَتَّى إِذَا أَدْرَكَهُ الْغَرَقُ قَالَ آمَنتُ أَنَّهُ لا إِلِـهَ إِلاَّ الَّذِي آمَنَتْ بِهِ بَنُو إِسْرَائِيلَ وَأَنَاْ مِنَ الْمُسْلِمِينَ

آلآنَ وَقَدْ عَصَيْتَ قَبْلُ وَكُنتَ مِنَ الْمُفْسِدِينَ

till when drowning overtook him, he (Fir`awn) said: "I believe that none has the right to be worshipped but He in Whom the Children of Israel believe, and I am one of the Muslims.'' Now (you believe) while you refused to believe before and you were one of the mischief-makers. (10:90-91)

And Allah says:

فَلَمَّا رَأَوْا بَأْسَنَا قَالُوا آمَنَّا بِاللَّهِ وَحْدَهُ وَكَفَرْنَا بِمَا كُنَّا بِهِ مُشْرِكِينَ

فَلَمْ يَكُ يَنفَعُهُمْ إِيمَانُهُمْ لَمَّا رَأَوْا بَأْسَنَا سُنَّتَ اللَّهِ الَّتِي قَدْ خَلَتْ فِي عِبَادِهِ وَخَسِرَ هُنَالِكَ الْكَافِرُونَ

So when they saw Our punishment, they said: "We believe in Allah Alone and reject (all) that we used to associate with Him as (His) partners.''

Then their Faith could not avail them when they saw Our punishment. (Like) this has been the way of Allah in dealing with His servants. And there the disbelievers lost utterly. (40:84-85)