FIRST SEE WHAT IS THE TIME DIFFERENCE BETWEEN THE WEBSERVER AND THE LINKEDIN SERVER
in linkedin.php there is a function [fetch] and do at the end of function
echo '<pre>';
print_r($return_data);
exit;
you will see the [oauth_timestamp] which your server is sending and at the $return_data print data there is a timestamp which linkedin server is sending.
convert both of them and see the difference you can do at this site. http://www.epochconverter.com/
at last
In OAuth.php file there is a function [generate_timestamp] which is returning a time().
By changing it to
#to avoid the error of
#oauth_problem=timestamp_refused&oauth_acceptable_timestamps=
#return time()+(difference of mints*sec);
return time()+(40*60);