Short answer: the Northern Lights can last anywhere from a few minutes to several hours, depending on solar activity and atmospheric conditions. Details

• Typical displays: many aurora sightings unfold in bursts of 15–30 minutes, with periods of quiet interludes in between. These active phases can repeat over the course of a clear night.
• Can last longer: during strong solar storms or geomagnetic activity, it’s common for the aurora to persist for several hours or even longer in favorable locations with dark skies and little light pollution.
• Variability: duration is influenced by solar wind intensity, the structure of the Earth's magnetic field at the time, cloud cover, and local light pollution. Even during a single night, you may see short flickers followed by longer curtains or bands.

What to watch for to maximize your chances

• Time of night: the best viewing window is typically between late evening and early morning (roughly 10 p.m. to 2 a.m., though this can vary by location).
• Location: areas with high geomagnetic activity and dark skies (far from city lights) improve visibility and length of displays.
• Weather and sky conditions: clear, dark skies are essential; clouds can completely obscure the aurora.

If you’d like, tell me your approximate location and month, and I can tailor the expectations for that region and season, including the typical activity levels you might expect and the best practice for maximizing viewing time.