I don't think it's available in Google Analytics, but there is a response graph in the "Crawl Stats" section of Google Webmasters Tools. (Webmasters Tools > Diagnostics > Crawl Stats) It shows a maximum, minimum and average time value for requesting pages from your site.
You can use the Page Speed browser plugin to show the loading time of your site.
The Site Performance info on Google Webmasters are sampling of your website over period of time to give you a rough estimate of how fast your site loads. And Google uses it as one of their input into the ranking algo.