That seems odd: except for the initial authorization, Apple doesn’t bill your card until it ships. If it’s shipping now, it would surely arrive before the end of the year even if Apple is conservative in the delivery schedule.
Right after I got my base model Air M1, I quickly realized it was way more fabulous than I expected and I’d use it more than just for testing, so I ordered a more loaded Air M1 replacement (16/512). The first one I ordered right after the keynote and got it exactly one week later. The second as of yesterday was still showing Dec 21-27 as the delivery, and I got an email from Apple saying it was delayed (so more than a month to deliver).
Then last week my card was charged and a day or so later Apple said it was shipping but still showed Dec 21 deliver date. It arrived in the States over the weekend from China. Fedex said delivery would be Dec 10, but to my delight it arrived today! I’m setting it up right now (it’s slowly syncing cloud data) and will send the base model back (Apple says I have until Jan 8 to start a return for it).
In my experience Apple usually underpromises and overdelivers, so there’s a good chance you’ll get it sooner than they say. If you get a tracking number, check that as it’s more accurate than what Apple says. I do get the feeling that these new machines are wildly popular and in short supply.