Timestamp

Timestamp 

Refers to the date and/or time measurement used, usually, at the beginning of a story or chapter, to denote when the events therein occurred. A timestamp fic is a drabble, ficlet or other short story written about some specific time before, during, or after an episode or other story. Timestamps themselves may be as precise as right down to the nanosecond or more generalized, such as ten years later.