title: php check online offline user status simply
body: <p>What is the best method to check if user is online or offline?
  in PHP,there is both functions:</p>
  
  <pre><code>time();
  </code></pre>
  
  <p>and</p>
  
  <pre><code>strtotime();
  </code></pre>
  
  <p>how to use them to check status ?</p>