Most of the mobile users find their concentration getting distracted after one or two seconds while browsing a website which does not load fast. However this is not practical and Google gives more importance to Above the Fold to be displayed in under one second so that the user gets the first glimpse of website. While the user views the portion above the fold the below portion can be rendered.
The loading of the website goes under the following stages before the viewer sees it
The first three sections is causing considerable delay due to the connectivity of network and the remaining two can be reduced with expertise. As most of the rendering happens in 3G network Google is keeping it as standard.
Server Response Time is the time taken by the server in returning the http request for the html file. For better user experience the redirection factor also need to be considered. This is because if there is another request for a redirected page chances are that the loading of page will take more time and the user might abandon the page. The TCP round trips also need to be minimum for loading the initial data required for the visibility of the web page.