It's very frustrating that au can't communicate any kind of estimated delivery time. But it can't be too simple, given all the possible stores that the devices could go to.
There's a site that aggregates people's reservations and helps to estimate delivery dates. It seems the one you ordered is still rather limited in stock, with only people having ordered a few minutes after reservations began have received theirs.
http://yoyakuget.com/iphone7-plus/au/html/index.html
Let's hope things start moving for us here, too, like it seems they are in the US.