tambah dan kurang jam

saya menggunakan

 public function kirim_email()
    {
    	$email= $this->DonasiModel->all3();
		//print_r($row);
        //load method template
        foreach ($email as $row) {
    	date_default_timezone_set('Asia/Jakarta');
   		$date= date('Y-m-d H:i:s');
        $time=$row['schedule_date'];
        if ($date>=$time)  {
        	$idemail=$row['email_id'];
    	$subject=$row['subject'];
    	$message=$row['message'];

		$emailpenerima			= $row['to_email'];
        $ci = get_instance();
        //$ci->load->library('email');
        $config['protocol'] = "smtp";
        $config['smtp_host'] = "ssl://mail.untukpalestina.com";
        $config['smtp_port'] = "465";
        $config['smtp_user'] = "admin@untukpalestina.com";
        $config['smtp_pass'] = "test$2012$";
        $config['charset'] = "utf-8";
        $config['mailtype'] = "html";
        $config['newline'] = "\r\n";

        $ci->load->library('email',$config);

       // $ci->email->initialize($config);

        $ci->email->from($row['from_email'],$row['from_nama']);
        $ci->email->to($emailpenerima);
        $ci->email->subject($subject);
        $ci->email->message($message);


		 if ($this->email->send()) {
            echo 'Email sent.';

            $this->DonasiModel->updateemail($idemail);
        }


    }

    else {
    	echo "error";
    }
}
    }

saya pakai codingan itu untuk kirim email otomatis d cronjob tapi hostingnya hanya bisa mengecek 5 menit sekali ga bisa perdetik nah masalahnya jika <= schduledate(data yg d db) semuanya kekirim bersamaaan padahal seharusnya setiap 6 , 18 ,24 jam jedanya nah bagaimana yah cara mengatasi itu