Above the fold content should load in less than a second. Corresponding to this new advice, Google has also released an updated version of it's PageSpeed Insights Tool, which helps web designers and developers check load-time issues with mobile websites. The updated tools now offers mobile scoring, ranking criteria and suggestions above desktop tools.
"[W]e must deliver and render the above the fold (ATF) content in under one second, which allows the user to begin interacting with the page as soon as possible. Then, while the user is interpreting the first page of content, the rest of the page can be delivered progressively in the background.”
The PageSpeed Insights Tool can be found at: https://developers.google.com/speed/pagespeed/insights/
The Suggestions Summary tool is a fantastic way to test and refine mobile websites--improving performance for responsive websites. Criteria items are documented and organized into serious impact, medium-level warnings and no significant issues found--indicated by icons (red exclamation point, yellow exclamation point and green check mark).