use strict ;
use warnings ;

my %Date_Time = (
  '03-12-2008' => { '0'  => { '8'  => { '5'  => 'a',
                                        '15' => 'b', },
                              '08' => { '22' => 'c',
                                        '05' => 'd', }, }, },
  '04-12-2008' => { '0'  => { '5'  => { '8'  => 'e', }, }, },
  '05-12-2008' => { '0'  => { '5'  => { '9'  => 'f', }, }, },
) ;

my @order ;
foreach my $date (keys %Date_Time) {
  my ($d, $m, $y) = split(/-/, $date) ;
  my $o = sprintf("%04d%02d%02d", $y, $m, $d) ;
  foreach my $sec (keys %{$Date_Time{$date}}) {
    foreach my $min (keys %{$Date_Time{$date}{$sec}}) {
      foreach my $hour (keys %{$Date_Time{$date}{$sec}{$min}}) {         
        push @order, $o . sprintf("%02d%02d%02d", $hour, $min, $sec)
                        . ":$date:$hour:$min:$sec" ;      
      } ;
    } ;
  } ;
} ;

@order = sort @order ;

foreach my $o (@order) {
  my (undef, $date, $hour, $min, $sec) = split(/:/, $o) ;
  print "Date=>$date $hour:$min:$sec = ", $Date_Time{$date}{$sec}{$min}{$hour}, "\n" ; 
} ;