Yes, session.gc_maxlifetime is a PHP_INI_ALL setting so it can be overidden in .htaccess:
php_value session.gc_maxlifetime 2000
Also make sure that <Directory>
entry in your Apache configuration supports override:
AllowOverride Options
It also may be possible that you misunderstood the purpose of this option. This option will not set the maximum life time of a session, it will set the amount of time after which the garbage collector will clean the session if it's not valid. This can be determined by a lot of factors, including access times, modification times, other INI options such as session.gc_probability and session.gc_divisor.
If you want to limit a session life time, use a proper mechanism for that, as described by @Gumbo in How do I expire a PHP session after 30 minutes.