The best time to go to Qaarsut is during the summer months, specifically from June to August, when the weather is mildest and daylight hours are longest.
During this period, temperatures are generally above freezing, making outdoor activities more comfortable. You'll experience nearly 24 hours of daylight in June and July, which is great for extended explorations of the surrounding nature. This is also when the ice in the fjords typically recedes, allowing for boat tours and easier access to remote areas.
For those hoping to spot the Northern Lights, late August and early September can also be a good choice, as the days begin to shorten, allowing for darker skies.