A general misunderstanding relating to Search Engine Optimisation is how quickly a website will be indexed by google.
Generally speaking, google suggest that it can take up to 6 weeks for this to take place. Personally speaking, I have never had a site take longer than 3 weeks, [artBreak] generally much faster. I have read forums where people claim that if you submit your sitemap.xml, and follow certain guidelines, that you can get things running swiftly. I tend to disagree, and from my experience the main influencing factor for how quickly google will index and rank your site lies with how important google thinks you are!
If you have no websites linking to yours, then you can assume that your site will not be regarded as important, and will not be crawled regularly. Any modifications you make won't be noticed for some time.
On the flip side of that, if you have many, important sites linking to you, it is safe to assume that your site will be crawled frequently, and modifications will be noticed quickly. Therefore, having those inbound links active from the launch of your site will speed up the indexing process. I have had sites indexed in a day before, after linking from the right places.
The crux is though, no matter what you read online, the rules are still made by google, so are subject to change at any time. A good web developer will build the site correctly, submit the domain in the necessary places, and work on inbound links from the start. Out side of that, the ball is in Google's court.