Google can't access site even after I update robots.txt.

Hi. I set up my WP site to discourage search engine crawling via the “Search Engine Visibility” checkbox while I was working on it. I then submitted it to Google after it was ready, but forgot to turn that feature off. When I realized this, I went to the WP dashboard and unchecked the “Discourage search engines from indexing this site” box. But it still isn’t updating in Google. How long does this take?

I have also installed the Google XML Sitemaps plugin and built the xml map.