What is the first day of the 2011 Star Wars advent calendar supposed to be?
I don't have it, but BrickLink already has inventories of all submodels.

According to them, day 1 is a Republic Cruiser. This is a mini version of 7665 — Republic Cruiser.

They do look quite similar for sets of a such different scale:




Sadly, Wookiepedia doesn't have a picture of a republic-class cruiser, but I suppose that's what it is.