Is once a quarter enough for a tech audit?
Keeping on top of problems or inefficiencies on your site is not just good practice for SEO, it’s just a good idea for your users in general — and that’s where a tech SEO audit comes in. Users and search engines are discouraged by things like broken links, slow loading times and badly formatted code, so you should fix them as soon as they are found.
There’s a broadly accepted rule of thumb in the industry that technical audits should be done at least once a quarter, but given the tools that we have at our disposal and the speed at which sites can be crawled/rankings change, I don’t think that goes far enough.
TLDR; fix SEO issues ASAP!
If you’re using something like Semrush then you can set it up to run an audit on a daily/weekly basis (and if you’re using Screaming Frog then you can just run it whenever, or even automate it from the command line (this is for another post, but it’s entirely possible to schedule Screaming Frog on a server somewhere and have it notify you when it’s done, and automatically share reports).
Given that both bits of SEO software I mention above give you a prioritised list of issues to fix/address, there is no reason whatsoever to not jump on any bigger SEO issues as they arise. As I say, an SEO issue is often more urgently a user issue, so you’d be daft not to fix things as soon as you’re aware of them.