Following script can be used to calculate difference between 2 dates.

sub date_diff {
    my %hash = @_;
    if($hash{start_day} && $hash{start_day}=~/^\d{1,2}$/ && $hash{start_month} && $hash{start_month}=~/^\d{1,2}$/ && $hash{start_year} && $hash{start_year}=~/^\d{4}$/) {
        if(!$hash{end_day} && !$hash{end_month} && !$hash{end_year}) {
            $hash{end_day}=strftime "%d", localtime;
            $hash{end_month}=strftime "%m", localtime;
            $hash{end_year}=strftime "%Y", localtime;
        } elsif($hash{end_day} && $hash{end_month} && $hash{end_year} && $hash{end_day}=~/^\d{1,2}$/ && $hash{end_month}=~/^\d{1,2}$/ && $hash{end_year}=~/^\d{4}$/) {
            
        } else {
            return 0;
        }
        use Time::Local;
        my @start_sec = (0, 0, 0, $hash{start_day}, int($hash{start_month})-1, $hash{start_year});
        my @end_day_sec = (0, 0, 0, $hash{end_day}, int($hash{end_month})-1, $hash{end_year});
        my $starttime = timelocal(@start_sec);
        my $endtime = timelocal(@end_day_sec);
        my %result;
        $result{s}=$endtime-$starttime;
        $result{i}=ceil($result{s}/60);
        $result{h}=ceil($result{s}/60/60);
        $result{d}=ceil($result{s}/60/60/24);
        $result{m}=ceil($result{s}/2629743);
        $result{y}=ceil($result{s}/31556926);
        return \%result;
    } else {
        return 0;
    }
}

my $result=&date_diff(start_day=>12, start_month=>6, start_year=>2015,end_day=>13, end_month=>6, end_year=>2015);
print "In seconds :- ".$result->{s};
print "In minutes :- ".$result->{i};
print "In Hours :- ".$result->{h};
print "In days :- ".$result->{d};
print "In months :- ".$result->{m};
print "In years :- ".$result->{y};

Output :-

In seconds :- 86404
In minutes :- 1440
In Hours :- 24
In days :- 1
In months :- 0
In years :- 0