before it starts to freeze, and it will lose its carbonation. The alcohol will cause it to freeze at a lower temperature than water but it will freeze eventually.

...the cork may pop, and you'll have a real mess in your freezer.

I speak from experience.

Keep it under an hour, and you should be okay.

... left it too long - it'll help prevent freezing.

Keep agitating the ice mixture, or spinning the bottle (if regular wine), and the wine/champagne will be chilled in minutes. That’s how we did it in the restaurant business, when short of a chilled bottle.

Edit: champagne corks are nothing to take lightly so the idea of putting a bottle in the freezer scares me. Came within an inch or two of losing an eye once from not gently removing the cork immediately after removing the little cage.