I am making stollen for the first time, and discovered I don't have time tonight to bake the dough. It is on its first rise right now. Can I keep the dough refrigerated overnight and complete the preparation in the morning?
Most yeast doughs develop additional flavor complexity if retarded in the refrigerator overnight, and there's nothing about a typical Stollen recipe that would cause anything to undermine retardation.
The only caveats: If you've already let the dough rise for several hours before retarding, there's a chance that you may not have enough food for the yeast to digest when the dough comes back to temperature, and the dough may not rise as much as you'd like. Also, if you've already shaped the dough with the almond paste inside, you'll need to take some care to seal in a bag without deforming the shape, and leave enough room in the refrigerator for the dough and the gases in the bag to expand.
But if you've only let the dough rise for an hour or so, as long as you refrigerate, the eggs won't be a problem, and you aren't likely to risk over-fermentation. In my experience, you usually need about 30-40 minutes time for the dough to become active again, assuming a moderately warm room.