The Night That Changed Everything: Analyzing Photos From Princess Diana’s Accident Scene

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.

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.

You will see it very.