Our punishment came to them at night or while they were sleeping at noon

And how many cities have We destroyed, and Our punishment came to them at night or while they were sleeping at noon.

[Qur'aan 7:4]

Ibn 'Aashuur makes an interesting observation when he writes:

وخصّ هذان الوقتان من بين أوقات اللّيل والنّهار : لأنّهما اللّذان يطلب فيهما النّاس الرّاحة والدعة ، فوقوع العذاب فيهما أشدّ على النّاس ، ولأنّ التّذكير بالعذاب فيهما ينغص على المكذّبين تخيَّل نعيمَ الوقتين

These two times from among the night and day were chosen because it is during these two times that people seek ease and rest, and therefore, the occurrence of torment during these two times is extremely severe on people and because the mention of torment during these two times spoils, for those who deny [Allaah and His Messengers], the thought of enjoying the pleasures of these two times.