====== following your code =====
use Data::Dumper;

#get Id_Codes based on entry time
#
my $feed_table_idcode = 
        $dbh2->prepare("SELECT id_code 
                        FROM $feed_table 
                        WHERE entry_time >= ?");

#get all columns for each id_code in another table                       
my $feed_table_ext_results = 
         $dbh2->prepare("SELECT * 
                         FROM $feed_table_ext 
                         WHERE id_code = ?"); 
                        
$feed_table_idcode->execute($time);

while (my @row = $feed_table_idcode->fetchrow_array() )
{
    my $id_code = $row[0];
    
    $feed_table_ext_results->execute($id_code);
    print Dumper $feed_table_ext_results,"\n";
}