Do they ship on weekends?
Possibly. Depending on where it's coming from. The Chinese facilities work Saturdays. But since it's coming FedEx, "ship" in this case just means FedEx will at least receive the notice of shipment information and maybe pick it up and transport it to the local Chinese FedEx station. Where it may sit until Monday, or FedEx, depending on how loaded their planes are, may fly it to Anchorage over the weekend. But FedEx will not count Saturday as a ship day, so no matter if it flies out today, which is getting close to tomorrow already in China -- meaning if it was going to ship it probably would have by now -- for purposes of 2-day delivery they will count Monday a the ship date, and it's unusual you'd actually receive it before Wednesday.
Note also Apple's shipping windows on their store are estimates, no guarantees, so it could be merely it hasn't shipped for whatever reason and they have no 24-hour ship commitment to meet.
So, if it's not your credit card, if it's not holding because it has new firmware they don't want to maybe end up in your hands today or early Monday before they release it to current owners via update, it will probably ship Monday, for Wednesday delivery, if it's two-day, which I think two-day is the standard shipping. Even if something went on with it this weekend, the order web site likely won't update until Monday either. Probably early Monday morning for you, since in China they will have had the whole day working with orders by the time you wake up.