I know you are specifically asking about the PHP timeout, but what no one else seems to have mentioned is that there can also be a timeout on the webserver and it can look very similar to the PHP timeout.
So if you have tried:
And you have checked with the phpinfo() function that max_execution_time has indeed be increased, then you might want to try adding this to .htaccess which will make sure Apache itself does not time out:
RewriteRule .* - [E=noabort:1]
RewriteRule .* - [E=noconntimeout:1]
More info here: https://www.antropy.co.uk/blog/php-script-keeps-timing-out-despite-ini-set/