The kitchen sink module is Date::Manip. It's pretty up front about where and when you should use it and why you might not - see the 'SHOULD I USE DATE::MANIP' section in the docs.

use strict;
use warnings;
use Date::Manip;

Date_Init ('DateFormat = NZ', 'TZ = NZST');

my $today = ParseDate ('today');

DateCalc ($today, '25 december ' . UnixDate ($today, '%Y')) =~ /\d+:\d
++:(\d+):(\d+)/;
print $1 * 7 + $2, ' sleeps until Xmas';
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Prints:

76 sleeps until Xmas
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On most *nix boxes you shouldn't need the Date_Init, but you will need it on most Windows boxes. Your time zone may be different than mine too. ;)