They will refresh it when they update their index next, assuming they have crawled your site beforehand.
It's depend upon crawling status of your site, more frequent crawl more information of your site on Google database.
once they crawl your site again they will update it. try bookmarking and other link building tactics. may be you can add your site in your sig. then your site will get crawled soon and the title will be updated.
Submit your site in digg.com and comments posting and also depend your site PR, Popularity and traffics
how often is your site updated ? How often does the google bot visit your site ? The change to take place on all pages will take a while. However, you may see the changes on your main page pretty soon. You can see the crawl frequency or get an idea about it in Google Webmaster Tools. /G
If your website is indexed in Google allready,then your site will be refreshed on Googles next update. This is generally quick,and doesnt take a lot of time.