This link explains how PAM works.[stijn@hermes ~]$ ldd /usr/bin/slim |grep pam
libpam.so.0 => /lib/libpam.so.0 (0xb7e1f000)
Old stuff that should not bother anyone anymore
As far as I can see there is nothing that a desktop user would care about in using pam. Even if that "ssh only certain times of day" sounds nice, it can be done with simpler ways anyway (crond switching ssh service on/off for example).