At Night or In the Night? - English Language & Usage Stack Exchange
1. The origin of "at night" to indicate a point of time and the usage of prepositions "in" and"at" In olden times, when the time expression "at night" was originated, night might have been thought as a point of time in the day because there wasn't any activity going on and people were sleeping that time unlike daytime.

Can we use "day and night time" instead of "day and night"?
4 Day and night time is not an idiomatic or set phrase (unlike day and night), but it can be used appropriately in certain contexts, particularly in technical ones. Here is a relevant usage I've found: The English word day can be used to refer to the time of daylight or to the unit of time that encompasses both day and night time.

Is 'Night an acceptable informal variant of "Good Night"?
The spoken use of "night" as an informal, familiar version of "good night" (wishing one a restful sleep) is common, but I'm not sure what the proper written equivalent is - if there is one.

What's the difference between “by night” and “at night”?
The expression by night is typically used to contrast someone's nighttime activities to their daytime activities, especially when the nighttime activities are unusual or unexpected.

At night or In the night - English Language & Usage Stack Exchange
What can I say about a thing happened at night? Someone stole my phone at night. OR Someone stole my phone in the night. Which one is right to say?

phrases - "Good night" or "good evening"? - English Language & Usage ...
If it's 7:30pm, which of these phrases is correct, Good night or Good evening?

What is a word for someone who is both an early bird and a night owl ...
Mediterranean? Lots of Mediterraneans have an afternoon siesta, so they could indulge themselves in such a preference. But Anglophones by and large don't go in for siestas, so there's probably not much call for a single term covering both "morning person, lark, early bird" and "night owl".

On this night vs In this night - English Language & Usage Stack Exchange
In this night of wonder or On this night of wonder, which is correct? The full context is God from heav’nly splendour Comes to earth below; In/On this night of wonder, The world is all aglow.

nouns - Can "nighttime" be used instead of "night-time"? - English ...
I forgot where but I saw the word "night-time" written like "nighttime". Now is that correct or accepted? Can it be written as a single word? I am specifically concerned about British usage. I did

What is an appropriate greeting to use at night time?
“Good night” or “good evening”? I am in the process of creating a software application which displays a greeting to users based on the time of day. I have come to a blank on what to display to the user when it is late at night. 'Good night, [user's name]' just doesn't seem right. So, what is an appropriate greeting to use at night time?