The word which indicates the time when an action takes place is called Adverb of Time. It satisfies the question, ‘when‘ or ‘at what time‘.
- I have not heard this song before.
- I received a letter from him recently.
- Lovely flowers bloom in the spring season.
- These children have been learning salsa for months.
- The sun shines brightly at noon.
In the above sentences, the highlighted words (before, recently, in the spring season, for months and at noon) show the time when their respective actions (heard received, bloom, learning and shines) take place. Therefore, they are adverbs of time.