If you are receiving a 504 Timeout Error from NGinx and are not using load balancing (or have already configured the proxy timeout see: https://www.vpsblocks.com.au/support/Knowledgebase/Article/View/347/13/increasing-timeout-on-nginx-load-balancer ), then you will need to configure the fastcgi timeout (this is used for calling PHP-FPM for example:

Edit the nginx.conf and add the fastcgi_read_timeout value to the location field for PHP files in webroot.

You will need to restart the NGinx node after saving the change.