It is not "first come, first served." There's no specific time it takes, as it is done based on the quality of the picture, the quality of the story, then we try to get a variety of breeds and kinds, from various places, etc.
It is not completely random. To that, I will add that we get more nominations for dogs and cats than any other kinds of pets, so if a family nominates, say, their sugar glider and their cat - with equally good pictures and stories - the sugar glider will probably be assigned a day before the cat. But not always.

We do try not too run "siblings" too close together - we want each pet to have a chance at revelling in his or her glory!