We all know that SEO isn’t a quick fix, it’s a long term marketing strategy and as such you need to be patient. When SEO is performed on your website you need to wait, monitor rankings and make tweaks because it could be months, or even years before you achieve the rankings that you desire.
This is of course depending on the competitiveness of your industry, and your budget for marketing. It ‘could’ take months and years, but then again, it could take a few days.
If a website has a decent history, a fair amount of links and a lot of pages, then it could jump in the rankings for the desired keywords in a matter of days after the SEO has been performed. Subtle on-page changes can have an immediate and drastic effect on some websites, causing them to leapfrog competitors, jump to page one or even rank #1 in Google days after they have had the SEO.
You of course shouldn’t expect this, but be prepared that it could happen to your website with a little expert search engine optimisation.