I am wondering whether we can declare session.gc_maxlifetime setting in .htaccess
for the one particular project instead of whole web server?
If so, how
As far I can see, the gc_maxlifetime value can be set anywhere:
http://php.net/manual/en/session.configuration.php
http://www.php.net/manual/en/configuration.changes.modes.php
So you could also set it via ini_set(...)
in a php file included in all your pages.
Anyway, I think your code in the .htaccess should work as well. Maybe you missed something else, for example
php_value session.save_path "/PATH/TO/SESSIONS"
where PATH/TO/SESSIONS is the path of a folder where you have 777 access permissions.