Check it first. Take the three phrases you believe customers would type and look at whether anybody types them, in your area, in meaningful numbers. For a plumber in Las Vegas the answer is obviously yes. For a specialised business to business consultancy selling something people have no name for, the answer is frequently no, and that is not a failure of your optimisation, it is evidence that discovery happens somewhere else for you. Businesses in the second category who spend a year on search work are optimising for traffic that does not exist.
If people do search, then yes, start early, because this is the channel where starting early compounds most. Search visibility accumulates over months rather than switching on, and a business that begins in month two has a year of accumulation by month fourteen while a business that begins in month twelve is starting from nothing at the point it most needs customers. The work is also largely permanent: a page that ranks continues producing without further spend, which is the opposite of advertising.
What to actually do first is narrower than most guidance suggests. Get your business profile complete and consistent if you serve a local area, because for local businesses that outweighs anything on your website. Then write pages that answer the specific questions people ask before buying, particularly about cost, comparison, and how to choose, since those attract fewer people and a far higher proportion who are deciding. Broad informational topics are heavily contested and increasingly answered directly by search engines before anybody clicks through.
Set expectations honestly about timing. Meaningful movement takes months, and anybody promising first position in weeks is either describing a term nobody searches or planning something that will eventually cost you the listing. The correct comparison is not against advertising, which produces results immediately and stops when you stop paying, but against building an asset that keeps working.
Measure it by enquiries rather than by rankings, because a first position for a term nobody searches produces nothing while a modest position for a high intent term can produce steadily. Rankings are easy to report and easy to feel good about, which is exactly why agencies lead with them. What you want to know is how many people contacted you having arrived from search, and that number is available in your analytics once conversion tracking exists.