title: What to use ? time() function or $_SERVER['REQUEST_TIME'] ? Which is better?
body: <p>Which one among these two time functions is better? </p>
  
  <p>I have a form on my website which is submitted by thousands of users every microsecond or less , thus , thousands of requests at the same time on my server.</p>
  
  <p>So I want to use the one which does not uses any sleep while execution. Also , how unique is <code>$_SERVER['REQUEST_TIME']</code> and <code>time()</code>? Do both change every microsecond?</p>
  
  <p>Will $_SERVER['REQUEST_TIME'] change every time I submit the form? Like , the time() function will change at every time difference. </p>
  
  <p>I need to give a unique url to the user for verification in which am appending the unique result generated from any one of the two? Also,  using microtime() would make PHP sleep? isn't it?</p>