Google will change the frequency of indexing based upon how often you add new content. Sites that have been stagnant for a while may only get indexed every few months. Sites that are updated daily usually get indexed several times per day. Each indexing only covers a small portion of the site, so make sure new content is linked to from the home page.
I don't think anyone knows how long it takes Google to adjust the frequency once you start doing updates. Google is as Google does.
If you are using WordPress, WordPress pings Google every time you add a new page or post. I frequently see Google spidering a page as I am making the final changes.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin