verify user activity

<?php

define("TIMEINTERVAL", 60); // define the interval in seconds

//we have a session, so I call it
session_start();

// if the user have not visited a page under an interval of 60 seconds, destroy the session
if ( (time() - $_COOKIE['session_time']) > TIMEINTERVAL ) {
  
  // log out the user from the session and redirect it to a page
  session_destroy();
  header('Location:a/page.php');
  
} else {

  //register or update a cookie if interval < 60 seconds
  unset($_COOKIE['session_time']);
  setcookie( 'session_time', time() );
  
}

// ... code ...

?>