There is really no fixed timeframe for an SEO strategy. What is guaranteed is that you always start by doing an audit of the website, sector, targeted user and a keyword research based on your business. From there you create a list of tasks and start dedicating hours every month to complete them. After a year or a year and a half, it is only about maintenance tasks and monitoring results. However, if the website is completely abandoned its performance will drop and you will have to start the hard work of “chopping stone” again.