microtime鼠标点击速度

Question

I am sure this has been cover by many people. So sorry for asking What will work to control a on click speed that someone can press. Need to not log the person out but need to slow the load on server as user seam to be using auto-clickers. i want to be-able to set in milliseconds. Exp 1)

<?php
// Checking Clicks
$now = microtime();
if ($_SESSION['click'] > ($now-0.05)) { 
$message = 
die('<img src="images/Unknown.png" /> <img src="images/n.png"    /> <img > 
src="images/Unknown.png" /> <div class="Fail">Error: Don\'t </div>');
 }
 $_SESSION['click'] = $now;

this works but will only do 1 sec microtime would not go below 1 sec

so i was thing ing this would be a workable 2)

 <?php
// Checking Clicks
$now = microtime(true);
if ($_SESSION['click'] > ($now < 100)) { 
$message = 
die('<img src="images/Unknown.png" /> <img src="images/Unknown.png" /> <img 
src="images/unknown.png" /> <div class="Fail">Error: Don\'t </div>');
}
$_SESSION['click'] = $now;

or just a loop

<?php
// Checking Clicks
$now = for($i=0;$i<100;$i++);
if ($_SESSION['click'] > ($now)) { 
$message = 
die('<img src="images/Unknown.png" /> <img src="images/Unknown.png" />  
<img 
src="images/Unknown.png" /> <div class="Fail">Error: Don\'t </div>');
}
$_SESSION['click'] = $now;

Thanks what would be best and what is wrong no need for time stamp in db