"But the Hour is their appointment," meaning: for the punishment of eradication. It refers to the disbelievers at the end of this nation, according to the interpretation of al-Hasan. "And the Hour is more catastrophic" than those afflictions by which previous nations were destroyed, "and more bitter," meaning: and more severe.
﴿بل السَّاعَة موعدهم﴾ أَي: بِعَذَاب الاستئصال، يَعْنِي: كفار آخر هَذِه الْأمة؛ فِي تَفْسِير الْحسن ﴿والساعة أدهى﴾ من تِلْكَ الأخذات الَّتِي أهلك بهَا الْأُمَم السالفة ﴿وَأمر﴾ أَي: وَأَشد.