I don’t have real-time access to space weather data in this moment. To give you a precise answer about how long the Northern Lights will last tonight, it’s best to check live aurora forecasts for your specific location, since visibility and duration depend on the current geomagnetic activity and cloud cover. What to check now

• Local geomagnetic activity: Look for a current Kp index forecast and expected activity levels for tonight (NOAA Space Weather Prediction Center or UK Met Office Space Weather). Higher Kp values generally mean more widespread and longer-lasting displays.
• Cloud cover: Clear, dark skies maximize visibility and the duration you’ll be able to observe the aurora.
• Geographic location and time window: The best viewing times are usually after astronomical twilight ends and before the first light of morning, but this shifts with latitude and local conditions.

How to maximize your chances

• Head to dark, open areas away from light pollution.
• Give your eyes 20–30 minutes to adapt to darkness.
• Be prepared to stay outside for several hours if a strong aurora is forecasted.

If you’d like, I can fetch the latest forecasts for a specific location you have in mind and summarize the expected duration window based on current data. Please tell me the city or coordinates you’re observing from.