#!/usr/bin/perl

use Data::Dumper;

my $time = time();
my $val  = 0.12205589;
my $element_name = "foo";

$element_stats_hash{$element_name}{'raw_data'}{$time} = $val;   # <--

print Dumper $element_stats_hash{$element_name};

__END__
$VAR1 = {
          'raw_data' => {
                          '1229382894' => '0.12205589'
                        }
        };