Salamun alaykum all,
Something's caught my attention just now about the usage of "nights" in the Quran. Our book is coherent, internally consistent, so we can find the usage of specific terms in other places in the Quran thus we can grasp the idea behind them.
Take a look at 19:10-11:
"[Zechariah] said, "My Lord, make for me a sign." He said, "Your sign is that you will not speak to the people for three nights, [being] sound."
"So he came out to his people from the prayer chamber and signaled to them to exalt [ Allah ] in the morning and afternoon."
To me, it seems that the usage of "nights" here could actually mean "day and night". If this is a sign for Prophet Zachariah (pbuh)... I mean I find it somewhat illogical that he could speak during daytime when the sun is up, and lost his ability to talk when it was night. Because that's the result if you take "nights" as "only nights not including daytime" here in this passage.
Logically, i think of whole 3 days here. If "ayyam" means "periods" in general (like the ayat about the creation of heavens and the earth), it could be understandable that Allah (swt) chose the word "nights" for further specification and elaboration, meaning "for 3 consecutive nights" that include daytime.
Just a thought.
Allah (swt) knows best.
Take care inshaAllah.