"On the Day they see it, it will be as though they had not stayed [in the world] except for an afternoon or its morning," meaning: or the forenoon of the day that shines upon the world.
﴿كَأَنَّهُمْ يَوْمَ يَرَوْنَهَا لَمْ يَلْبَثُوا إِلَّا عَشِيَّة أَو ضحاها﴾ أَيْ: أَوْ ضَحْوَةً تُضْحَى الدُّنْيَا.