Currently this defaults to 5 hours (based on the code here).
You can override this by launching chrome with the extensions-update-frequency command-line parameter, which is the frequency in seconds. And you can go to chrome://extensions, tick the Developer mode checkbox at the top right, then press the Update Extensions Now button
Chrome docs doesn’t specify this 5 hour value though, so it could change in future versions without notice:
Every few hours, the browser checks whether any installed extensions
or apps have an update URL. For each one, it makes a request to that
URL looking for an update manifest XML file.