As a general rule of courtesy, it's best to avoid vacuuming late at night if you live in an apartment above other people. The specific acceptable time may vary depending on the building's rules, local regulations, and the tolerance of your neighbors, but a good guideline to follow is to refrain from vacuuming past 9 or 10 PM.
Most residential buildings have "quiet hours" during which residents are expected to keep noise to a minimum to avoid disturbing others. These hours typically begin around 9 PM or 10 PM and last until the morning, often around 7 AM or 8 AM.
To be considerate to your downstairs neighbors, try to complete your vacuuming and other potentially noisy activities during the daytime or early evening. If you're uncertain about the specific rules in your apartment complex, it's a good idea to consult your building management or check your lease agreement for any guidelines regarding noise and quiet hours.