I'd be more worried about them delivering an empty box. I was reading on the Apple Forum last night and there have been dozens and dozens of empty boxes delivered where the phone was actually stolen from the box. Rather it was the driver, done at the regional hub or local FedEx station no one knows. It takes weeks to get it sorted out though. What a mess. Not telling you this to scare you, but signing those releases you do release Apple from all responsibility. I won't do them.
In regards to your concern, the short while it maybe in the heat won't impact your battery. It will be just fine. Let us know how it goes once you get it. Nothing like getting a new toy!