use strict;

use constant BASE => 10000;

print diff("23:59:59.9999", "00:00:00.0000"), "\n";
print diff("00:00:00.0000", "23:59:59.9999"), "\n";

sub diff {
    my ($before, $after) = @_;
    my ($h1, $m1, $s1, $ss1) = ($before =~ m/(\d+):(\d+):(\d+)\.(\d+)/);
    my ($h2, $m2, $s2, $ss2) = ($after  =~ m/(\d+):(\d+):(\d+)\.(\d+)/);
    my $diff = (($h2-$h1)*3600 + ($m2-$m1)*60 + $s2-$s1)*BASE + $ss2-$ss1;

    return ($diff >= 0) ? $diff : $diff + (86400 * BASE);    
}