#!/usr/bin/perl
use strict;
use warnings;
use File::stat;
use Data::Dumper;
use Time::localtime;
use File::Find::Rule;

sub get_files {
    my @dirs = ('/home/user/Monks' , '/home/user/Monks/mySubDir'); # add more
    my $level = shift // 2; # level to dig into

    my @files = File::Find::Rule->file()
    ->name('*.xml', '*.txt') # add your file(s) extension(s)
    ->maxdepth($level)
    ->in(@dirs);

    return @files;
}

my @files = get_files();

my %hash;
for (@files) { $hash{$_} = ctime(stat($_)->mtime); }
# or # for (@files) { $hash{ctime(stat($_)->mtime)} = $_; }

print Dumper \%hash;

__END__

$ perl test.pl
$VAR1 = {
          '/home/user/Monks/ArabicCharacters/original.txt' => 'Fri Jul 28 13:21:04 2017',
          '/home/user/Monks/out.txt' => 'Thu Jul 20 13:29:41 2017',
          '/home/user/Monks/filter.txt' => 'Thu Jul 13 11:03:53 2017',
          .
          .
          .
        };