Probably not much. I remember seeing a comment from someone that works at cloudflare, saying that they could deploy changes within hours.

edit:

>Fortunately, we have an advantage here, in that we directly control the machines on which our system runs. We have automated almost our entire build and release process, so the moment a V8 patch is published, our systems automatically build a new release of the Workers Runtime and, after one-click sign-off from the necessary (human) reviewers, automatically push that release out to production.

>As a result, our patch gap is now under 24 hours. A patch published by V8's team in Munich during their work day will usually be in production before the end of our work day in the US.

https://blog.cloudflare.com/mitigating-spectre-and-other-sec...

We patched when we were notified. And we have a pretty robust model around Workers that is meant to deal with this possibility.

Or anything running on NodeJS?