How long is an SEO campaign?
An SEO campaign theoretically never ends. From a business point of view, the aim of the campaign is to build visibility for virtually all keywords related to a given company and its offer.
Potential customers are changing their behavior and using more and more phrases. That's why SEO is an ongoing job.
Of course, an SEO campaign has its stages. It's intense at first because the site usually doesn't get enough traffic. Later, work on the website is limited to adding new content, sponsored articles (links) and periodic optimization.
In the final phase, the goal of the campaign is to maintain traffic and optimize conversions - i.e. increasing the number of inquiries / sales with the same number of visits to the website.