I gave them a call when i hadn't heard back after two days. they had me down for my first choice day, but said they'd just hadn't sent out confirmation messages yet. i got my confirmation the next day or so along with messages from the hotel, confirming my stay. interviews are simply to important to hope that your message didn't get lost or overlooked, so i'd recommend calling. i'm sure they understand that we're anxious and trying to coordinate many interviews at the same time. best wishes!
