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. 0 Perhaps dawn is what you are looking for?

Understanding the Context

It's the period after night, and just before sunrise, the beginning of morning twilight. It's recognized by the presence of weak sunlight, when the sun is still below horizon. There are also more technical definitions of dawn, available at Wikipedia. 1.

Key Insights

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. At Night or In the Night? - English Language & Usage Stack Exchange 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. 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.

Final Thoughts

word usage - 1 o'clock in the morning OR 1 o'clock at night? - English ... Can we use "day and night time" instead of "day and night"?