use Data::Simple qw(date);

my $start = date('1940-02-12');
my $min   = date('2007-05-01');

my $end   = date('2010-08-23');
my $max   = date('2008-04-30');

$start = $min if $star < $min;
$end   = $max if $max  < $end;

print "Duration: ", $end - $start, " date\n";