These routines are the inverse of built-in perl functions localtime() and
gmtime(). They accept a date as a six-element array, and return the
corresponding time(2) value in seconds since the system epoch (Midnight,
January 1, 1970 UTC on Unix, for example). This value can be positive or
negative, though POSIX only requires support for positive values, so dates
before the system's epoch may not work on all operating systems.

WWW: http://search.cpan.org/dist/Time-Local/