(Ambiya') 21 : 97
وَاقْتَرَبَ الْوَعْدُ الْحَقُّ فَإِذَا هِيَ شَاخِصَةٌ أَبْصَارُ الَّذِينَ كَفَرُوا يَا وَيْلَنَا قَدْ كُنَّا فِي غَفْلَةٍ مِنْ هَٰذَا بَلْ كُنَّا ظَالِمِينَ
And the true promised Time is approached; then suddenly the eyes of those disbelievers will be staring in horror: "Oh woe to us; we had been heedless of this; nay, we were the wrongdoers".
The true promised Time mentioned in verse is Doomsday. See explanation 2: 254; 9: 84-85, 125, and 18: 100-101.