I've only done two preorders but I've had different experiences. When I ordered my 5, I went through Apple and it was delivered by FedEx. Unfortunately, I wasn't home and they left a slip at the door and I went down to the FedEx sorting facility at around 8pm, stood in a huge warehouse, and asked the guys there if I could get my package. They were awesome and located it for me.
I just ordered my 6 through Verizon and it's also going through FedEx but I work from home so I don't have to worry about missing it. And from what I recall, FedEx is usually here earlier in the day. Probably before 3pm.
As far as I've known, they've always been strict about getting a signature for delivery.