I suggest that you conduct an audit of your heading structure at least once every three months. This cadence is effective because it will identify and fix issues before they have a chance to compound and create a larger problem. Content is often updated, new sections are created, and your templates are also changed. As a result, heading drift occurs without being detected until it becomes very noticeable. In my experience, I have seen duplicated H1 tags, out of order (H2) tags created, and design changes that cause some heading tags to become "styling hacks," as a result, within a matter of a few weeks. Conducting an audit once every three months should help to ensure that your heading structure aligns with your target audience's search intent and current company priorities. It is also a very quick process to conduct an audit of your heading structure once every three months as you can use a browser extension to scan all of your websites key templates and identify any issues within a matter of minutes. If you do not conduct an audit of your heading structure at least once every three months, you run the risk of structural debt building up and/or creating a more complex heading structure. Alternatively, you may find that you will be conducting an audit of your heading structures too often and may become overwhelmed with managing multiple audits if your company publishes at a very high volume.
As with many things in life, in marketing and SEO the most common answer is: it depends. Generally speaking, I recommend doing it at least once a year. And here, I would suggest carrying out a complete audit of the website as a whole. In some industries that depend heavily on organic traffic and are more competitive, I would increase the frequency to twice a year. If the algorithm or trends change frequently, we could even consider doing it more often. If we are getting good results and we are not in an overly competitive sector, perhaps we can stretch it beyond a year. On the other hand, if we have suffered a penalty or a widespread drop in rankings, we should probably carry it out immediately. In the end, as with all business decisions, we need to measure the real impact on the business and try to optimize the frequency accordingly.