Check your server logs to see how often they are visiting you. Just because they crawl doesn't mean that crawl is going to result in immediate changes to the index. They have many datacenters. Updates come in all sizes.
There is no specific time period for the Search Engine Positions (SERPS) to update, they are updated constantly just like Page Rank. http://www.adwordaffiliate.co.uk/seo/seo-faq/serps/
Crawling would depends on the site optimization. If your site has new contents, have many backlinks and always see by search engine your site can be indexed everyday.
Yes, google do regular indexing depending especially on the amounts of new sites being index per day....They crawls on regular basis.
google crawls 20k + pages per day from our site - although the rate at which it is added to the index is another story... that part i can't figure out.
google visits every web site according to their backlink power . when it visits your site, it gets a copy of your pages to google index