If it's made right it doesn't...
Of course it does. It needs time for the flavour molecules to break down and mix with everything else.
Though to answer the OPs question.
How long is a piece of string?
Maybe it was a fresh shipment, maybe they've had it for a while... maybe they did have it for a week, but it had been sitting in the light. Maybe it had been sitting in a dark box for a week before being put on the shelf.
Who knows. Most e-juice manufacturers will state whether the juices are pre-steeped and most retailers will just sell the stock and buy in new, to whatever the demand of the product is.
So the answer really is, it could be steeped, it could not.
Personally any juice I buy, I'll try a few toots, give it some air, close it up and leave it in the dark for a 3-4days.