The new copy is pushed to the CDN pretty quickly. I don’t know much about vercel. But the benefit of CDNs is that there is a 1:N relationship between you and the edge servers, and then an N:M relationship from the edge servers to the users.

So there are a lot more servers much closer to people using your site. Pushing a new copy from “you” to each edge server is pretty straightforward. I imagine Vercel does it pretty quickly, but sometimes the edge server could poll for changes maybe once a minute, which is pretty cheap to do.