Depending on which you choose, there'll be a config-file either in your HOMEDIR called .<name_of_screensaver_rc> or in /etc. If the file resides in /etc, copy it in your HOMEDIR and name it .<name_of_screensaver_rc>.
In that file will be something like a timeout value.
Example from my .xscreensaver-file:
timeout: 0:02:00 # logs me out after 2 minutes without action
Hope you'll figure it out! regards
chenn