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.

word usage - 1 o'clock in the morning OR 1 o'clock at night? - English ...
Do you think '2 o'clock in the morning' might somehow actually mean '2 o'clock in the afternoon', as that's the only alternative? I suppose I can see your point if someone says '11 o'clock at night' for 11pm, but again, unless you're above the arctic circle, the distinction with '11 o'clock in the morning', or any normal representation of 11am, is surely clear.

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 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?

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.

nouns - Can "nighttime" be used instead of "night-time"? - English ...
Can "nighttime" be used instead of "night-time"? Ask Question Asked 11 years, 7 months ago Modified 6 years, 2 months ago

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?

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.

meaning - Is the usage of “night and day” as “completely different ...
Similar to day and night, except it implies an improvement of the situation rather than a deterioration. So my question: Is the usage of ‘night and day” in the meaning of “completely different” popular, or still on the sideline? Because I don’t find it in any of Cambridge / Oxford / Merriam –Webster English Dictinoary.