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. What can I say about a thing happened at night?

Understanding the Context

Someone stole my phone at night. OR Someone stole my phone in the night. Which one is right to say? “Good night” or “good evening”?

Key Insights

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?