On average, a single screenshot should take approximately one minute per browser. Some web pages may take up to a minute and a half, whereas the fastest seen are around a half a minute.
These figures do not include the time waiting on a configuration (like Mac OSX 10.6) to become available during peak hours, nor does it include the time for the configuration to boot up and begin running the screenshot process, which is usually only a few seconds.
The responsiveness of the website host, the speed of internet routing, the number of elements on the page, and the browser’s rendering time can affect how quickly a page loads and is deemed ready for screenshots. As a screenshot test runs, the browser is scrolled and the screens are captured in order to append together the final full page screenshot, so the length of the page is another factor in the overall timing.
From an accounting standpoint, you are only charged for the time the screenshot process begins up until the time the full page screenshot is complete. No time is charged for the loading or tear down of the configuration before and after the test is run.