Why don't you store the values individually as keys, and format them directly when printing?

I think of a structure ordered by "logical size" of each value:

%Date_Time = (
  Year => {
    Month => {
      Day => {
        Hour => {
          Minute => {
            Second => 1,
          },
        },
      },
    },
  },
);

for my $year ( sort keys %Date_Time ) {

  for my $month ( sort keys %{ $Date_Time{$year} } ) {

    for my $day ( sort keys %{ $Date_Time{$year}->{$month} } ) {

      my $time_r = $Date_Time{$year}->{$month}->{$day};

      for my $hour ( sort keys %$time_r ) {

        for my $minute ( sort keys %{ $time_r->{$hour} } ) {

          for my $second ( sort keys %{ $time_r->{$hour}->{$minute} } 
+) {

            printf "Date: %d-%d-%d %02d:%02d:%02d\n",
             $day, $month, $year, $hour, $minute, $second;
         }
      }
    }
  }
}
[download]