Words such as then, next and after are known as?

future perfect tense i believe. Have a nice day. :)

Third person omniscient.

Explanation:

There are various forms of narration in literature and other forms of literary works. Based on the question asked, the omniscient third person narration is the form of narration that has full knowledge of all the characters. The narrator is not part of the story nor does he interact with the characters. But he is capable of revealing and narrating even the thoughts and feelings of the various characters. It is through him that the readers are able to have a bird's eye view of the story. He is an important structure and literary device for the development of the characters as the story develops.