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.
For example, 'Imagine a future where time travel is common, but has strict rules.' To make use of this, think about what those rules might be and how they affect people's lives. Also, consider the adventures and challenges that could arise from such a situation.
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.