I think people often look at SEO results too narrowly. you can start seeing signs earlier than actual traffic or revenue, impressions increasing, pages getting indexed, keywords moving from nowhere to page 2/3, etc.
these are the first signs that the strategy is working. the bigger mistake is expecting meaningful traffic in a few weeks and giving up before Google has had enough time to trust the site. the timeline really depends on the niche, competition, authority, and how consistently you work on it.