Is it possible to write a novel on short notice?

stephen king in his cocaine days could

Charles Bukowski wrote his first novel "Post office" in less than a month.

Yes if you put all your time aside for it multiple hours a day then it's possible.

There are a few very experienced writers who can do this. The rest of us cannot.

If I recall, William F Buckley once wrote an enter book in less than a week from when he got the idea, and got it published (and it sold enough copies to make money too).

It is possible to quick write everything in one go and edit everything when finished. It's possible, but it depends on how long and how much writing is being done.

Possible? Yes. Healthy? No.