"Product Replacement Pending" How long?

I sent my iphone 3GS in after recieving the empty shipping box from apple about a week ago. It arrived at the apple office yesterday and the repair status says that the issue has been identified. It's on step 3 right now - Product Replacement Pending. It has been like that since yesterday evening and I was wondering how long it will take until they ship me my refurbished iPhone? How long does the "Product Replacement Pending" step usually take?