Well if you don't mind a little bit of handywork, you can get along fine with the core module Time::Local. That module implements the functions timelocal() and timegm(), the inverse functions of respectively localtime() and gmtime().

One thing you should not forget, is to decrement the month value: January is month 0, December month 11. 4-digit years are fine, though you're allowed to subtract 1900.

Here's some sample code, that calculates the time value for some date, at noon, GMT:

my $datestring = "2003/11/19";  # input

use Time::Local;
my($y, $m, $d) = $datestring =~ m<^(\d+)/(\d+)/(\d+)$>
  or die "Not a valid date";
my $time = timegm(0, 0, 12, $d, $m-1, $y);
print "The time value is $time, for " . gmtime($time) . "\n";
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Result:

The time value is 1069243200, for Wed Nov 19 12:00:00 2003

p.s. The results are limited to the date range that applies to Unix time, thus to localtime and gmtime, i.e. from 1970 to 2035, roughly; or the equivalent on your platform — on the Mac, that's from 1904 to around 2035.