According to this answer, the session.gc_maxlifetime
is based (as of PHP 4.2.3) on the last modified date of the session:
Note: If you are using the default file-based session handler, your filesystem must keep track of access times (atime). Windows FAT does not so you will have to come up with another way to handle garbage collecting your session if you are stuck with a FAT filesystem or any other filesystem where atime tracking is not available. Since PHP 4.2.3 it has used mtime (modified date) instead of atime. So, you won't have problems with filesystems where atime tracking is not available.
I can find nothing on the official documentation about that, the note seems to be disappeared, so is this still true?