Here's a subroutine that you can send those two time stamps to for the desired output (returns 0 if no intersecting time):
use Modern::Perl;
use Date::Calc qw/ Date_to_Time Time_to_Date /;
say intersectingTime(
'2012-08-17 12:00:00',
'2012-08-17 13:00:00',
'2012-08-17 09:00:00',
'2012-08-17 12:30:00'
);
sub intersectingTime {
my ( $s1, $e1, $s2, $e2 ) = map Date_to_Time( /\d+/g ), @_;
my $tStart = $s1 > $s2 ? $s1 : $s2;
my $tEnd = $e1 < $e2 ? $e1 : $e2;
$tEnd <= $tStart
? 0
: sprintf '%4d-%02d-%02d %02d:%02d:%02d for %02d minutes',
Time_to_Date( $tStart ), ( $tEnd - $tStart ) / 60;
}
Output:
2012-08-17 12:00:00 for 30 minutes