php - How to set maximum run time using interval on each loop?

Question

Good morning! I need to send some email reminders according to some conditions. I built a script that queries the information in the database (Mysql) and triggers the emails. The script is working very well, however, from what I saw in some forums over the internet, it is interesting to set an interval between sending an email and another. I put interval of 20 seconds between after each upload, but before that I set a maximum execution time of the script, and for what I saw when I use the function set_time_limit() the function sleep() is ignored.

Follow the logic of my script below:

// faço a consulta na base de dados (MySQL)
if ($stmt->rowCount() > 0) {
   $result = $stmt->fetchAll();
} else {
   exit;
}

// controlar tempo máximo de execução do script
$qtd_email =  $stmt->rowCount();
$time_email = 20;
$segundos = ($qtd_email * $time_email) + 20; // adiciono 20 seg de folga
set_time_limit($segundos);

foreach ($result as $rs):

   // mensagem do e-mail

   // envia o e-mail

   // Ao terminar 1° loop, aguarda 20 segundos para o próximo
   sleep($time_email);

endforeach;

In that case the function sleep() is being ignored. The execution time of the script on the server that will host the application is at most 60 seconds, so I need to use set_time_limit(). In case anyone knows a way around it, I’m very grateful!

If there is another way to do it, I am also open to suggestions. Thank you from now!