I think it's different depending on where in the cycle you are. For example, a lot of people who ordered early enough to get launch-day delivery reported getting charged a day or two before. In my case, both with the iPhone 7 Plus and Apple Watch Series 2; both which arrived several weeks after launch, I got the pre-auth and "Preparing for Shipment" the same day, with the item listing "shipped" by the next day. It wasn't more than a couple of days after I got the charge that I got the product.
BUT!
1) Not a Mac
2) Not a day-one-delivery
3) We don't have a 'launch day' for these Mac's, just a broad "two or three week" window.
I think point 3 complicates things a bit.
It's funny. I've been checking all day. Absolutely nothing I do is going to change when it comes in. Knowing that it's shipped or not is futile and useless. But I'm still not gonna stop doing it!