This is probably the million dollar question of search!  We get asked this with every new client and every lead. 

There are quite wide variations on the timescales in achieving resultes through search engine optimisation due to many different factors.  The search engines all have varying requirements and various keywords are more competitive than others. 

In some circumstances a site could show results from search engine optimisation, within 48hrs of being crawled by the serach engine spiders. In other circumstances it can take upto 14 days before anything is visible.  Fully optimised results will take upto 9 months for new sites and six months for sites with highly competitve keywords.

It is advised that a search engine optimisation campaign should be undertaken for a minimum of 6 months.