$ perl -e '
    use strict;
    use warnings;
    use Data::Dumper;
    my $VAR1 = {
        Total => { month1 => 0, month2 => 0 },
        Tom => { month1 => 17, month2 => 1 },
    };
    my $VAR2 = [
        {
            Total => { week1 => 0, week2 => 0 },
            Harry => { week1 => 0, week2 => 5 },
        }
    ];
    my %joined_FS = (
        Total => {
            %{delete $VAR1->{Total}},
            %{delete $VAR2->[0]{Total}},
        },
        %$VAR1,
        %{$VAR2->[0]}
    );
    print Dumper(\%joined_FS);
'
$VAR1 = {
          'Tom' => {
                     'month1' => 17,
                     'month2' => 1
                   },
          'Total' => {
                       'month2' => 0,
                       'month1' => 0,
                       'week2' => 0,
                       'week1' => 0
                     },
          'Harry' => {
                       'week2' => 5,
                       'week1' => 0
                     }
        };