Well, with short story prompts for fiction, you should consider it as a springboard. If the prompt is about a time - traveling event, start imagining the character who experiences it. Is it a scientist? A regular person? Then, think about the rules of time travel in your story. How does it affect the character? What is the character's goal in this time - traveling journey? You can also add sub - plots related to the character's personal life before and after the time - travel.
How about 'A young adult has to solve a mystery that has haunted their family for generations.' This could lead to all sorts of adventures and character development. There could be hidden clues, long-lost relatives, and unexpected twists.
You can look for inspiration in your daily life. Observe people, events, and emotions around you. Also, reading a wide variety of books and articles can spark ideas.