How many inbound links does your site have?

If you have an old site with no links, this will add to the time you need to wait. If you have a number of links already, Google will probably be in to check out things within a week or so of updating.

How optimized is your site before SEO?

If your established site has no optimization in place at all, and has navigation that is blocking search engine spiders, sometimes opening the site up can result in a rather quick turn-around for results.