Perhaps something like this:

sub delta_time {
   my ($start, $end) = @_;
   $start = substr($start, 0, 2) * 60 + substr($start, 2, 2);
   $end   = substr($end,   0, 2) * 60 + substr($end,   2, 2);
   return $end - $start;
}

my ($minutes, $hours);
$minutes = delta_time '0930', '1145';
$hours = int($minutes / 60);
$minutes %= 60;

print "Delta: $hours:$minutes\n";
[download]

Cheers,
CombatSquirrel.

---

Entropy is the tendency of everything going to hell.