"The word which expresses time and tell us when something happens is called 'adverb of time'. "

Adverbs of time' tell us when an action happened. (The test question is when?).

» The test question 'When?' : We must go now.

'Adverbs of time' are usually placed at the end of a sentence. You can place it at the start of the sentence to put a different emphasis on the time.