Sweet? Means these are dessert?

Fruit verenikes are are typical Eastern European fare--they are not non-traditional! Caudia Roden includes a recipe for fruit verenikes, including a cherry variation (a teaspoon of sugar and an optional pinch of cinnamon can be added before filling and sealing). There are several food bloggers featuring Eastern European foods that include recipes as well. With sour cream spooned over, they can be part of a dairy dinner. With sugar, they can be a dessert.

There’s no sugar in the dough, and the recipe calls for sour cherries. So it doesn’t have to be sweet. (Sprinkling sugar on them is optional.) You could serve them as part of a cheese course as a tart counterpoint to a rich cheese. I agree that there is no right or wrong time to serve them.

Traditional Russian dumplings are savory, filled with meat.

These aren't traditional with their sweet flavor profile. One of the tags on the recipe is "breakfast" which makes sense because of the American obsession with dessert-like breakfast items.

So serve it whenever your dinner guests would appreciate something sweet, whether it be breakfast, lunch, dinner or a snack. There is no right or wrong time to serve these since A.) they're non-traditional and B.) the point is to satisfy the people at the table.