The amount of time you will have to wait will depend on which techniques are employed in your efforts to optimize your website. Assuming you've rebuilt your site and loaded it onto your server, replacing the old files, you need to be prepared to wait anywhere from a few days (if you use a pay-for-inclusion service) to a few months.

If your site has already been on the Web for some time, and is already listed in all of the major directories, then you will probably begin to see improvements in your search engine rankings within 4-6 weeks.