Configure max execution time in PHP-FPM

Edit php.ini

max_execution_time = 300

Edit www.conf file from php-fpm

request_terminate_timeout = 300

Edit nginx virtual hosts file for your website

location ~ .php$ {
include /etc/nginx/fastcgi_params;
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_read_timeout 300;
}

Restart php-fpm and nginx

service php-fpm restart
service nginx restart