Fronting

Definition: Any construction in which a word group that customarily follows the verb is placed at the beginning of a sentence. Also called front-focus or preposing.

Fronting is a type of focus strategy often used to enhance cohesion and provide emphasis. 

 http://www.eltbase.com/notes.php?id=538
http://www.ejerciciodeingles.com/enfasis-ingles-fronting/

I went home at 4 o’clock. ( important information)

At 4 o’clock, I went home. ( important information)