Google crawls site A every hour and site B once in a day. site B writes an article,site A copies it changing time stamp. Site A gets crawled first by Google bot. Whose content is original in Google eyes and rank high?

Well, Site A will be shown in results faster than site B as Google came to knew abt the article from site A then site B. Site B needs to meta tags mentioned by my colleagues above to let Google knows that the content is originally written by Site B, increase crawl rate (http://www.searchenginejournal.com/…). Once your carwl rate improve, Site B can easily beat Site A for its content.