A deadline nobody is told in advance
A description of the moment repentance stops being accepted.
لاَ تَقُومُ السَّاعَةُ حَتَّى تَطْلُعَ الشَّمْسُ مِنْ مَغْرِبِهَا فَإِذَا طَلَعَتْ مِنْ مَغْرِبِهَا آمَنَ النَّاسُ كُلُّهُمْ أَجْمَعُونَ فَيَوْمَئِذٍ لاَ يَنْفَعُ نَفْسًا إِيمَانُهَا لَمْ تَكُنْ آمَنَتْ مِنْ قَبْلُ أَوْ كَسَبَتْ فِي إِيمَانِهَا خَيْرًا
The Hour will not come until the sun rises from the west. When it rises and people see it, they will all believe, but that is when no soul will benefit from believing if it had not believed before.
The full narration
It is narrated on the authority of Abu Huraira that the Messenger of Allah (ﷺ) said:The (Last) Hour shall not came till the sun rises from the place of its setting And on the day when it rises from the place of its setting even if all the people together affirmed their faith, it would not be of any avail to one who did not believe previously and derived no good out of his belief
Source
Ṣaḥīḥ Muslim · 396
- Agreed upon as authentic (al-Bukhārī / Muslim)