Because these are so similar to Vanillakipfel I suspect that they would last a long time (at least 3 weeks). We always make Vanillakipfel at least a week before eating them to mellow the flavor and develop the texture. ← My Greek mother-in-law makes kourambiedes every Christmas to give as gifts, and not only does she dust hers with powdered sugar, as soon as they come out of the oven, she packs them in powdered sugar in little gift tins. They last an unbelievably long time, supposedly because the powdered sugar is so fine that it keeps out any air. The reasoning may be a family myth, but I can tell you, I've opened a tin of her Christmas cookies the following July, and they're still perfect.