I learned my lesson 2 years ago with the 6+ and ordering through AT&T, pre-ordered on Sept 9, 2014, and was told an early November delivery date, I sat on it for 4 weeks thinking it would come sooner, I ended up canceling the order and going to an Apple store and buying it outright.
Fast forward to this year, iPhone 7+, I pre-ordered on Apple.com early in the AM on Sept 9, had an estimate delivery date of 10/4-10/10, so I was browsing iStockNow.com, saw a local Apple store had the 7+ I wanted, canceled my pre-order and re-ordered it on Apple.com for in store pickup.
Some people who pre-ordered early in the AM on 9/9 got their phones on release day, but the majority of orders are pushed off until late Sept, early Oct and some even early Nov. I say if you have an Apple store near by, cancel your pre-order and just wait for the store to have some in stock (unless you're talking about Jet Black, there is a global shortage of those right now).