use strict;
use warnings;
use POSIX qw(mktime difftime ctime);

my $previous = '10111623';
my $current = '10111705';

my $time1 = mktime( 0, 0, $4, $3, $2 - 1, $1 + 100 ) if $previous =~ m/(\d\d)(\d\d)(\d\d)(\d\d)/;
my $time2 = mktime( 0, 0, $4, $3, $2 - 1, $1 + 100 ) if $current =~ m/(\d\d)(\d\d)(\d\d)(\d\d)/;

printf("%s - %s = %d seconds\n", ctime($time2), ctime($time1), difftime($time2, $time1));