title: RegEx in php to match disallowed chars
body: <p>I have a problem with matching "bad" lines. Every string with length outside of 6-8 character range and does contain any characters other than numbers or ":" should be matched. See examples below.</p>
  
  <p>These strings should <em>not</em> be marked:</p>
  
  <pre><code>001000
  000000
  236849
  576852
  09:34:24
  23:59:59
  00:00:00
  </code></pre>
  
  <p>I only want these three to be marked:</p>
  
  <pre><code>123456789
  67855jkl
  5678lk
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>if (preg_match('/^(?![0-9]{2}:[0-9]{2}:[0-9]{2}).*$|(?![0-9]{0,8})$/', $user-&gt;start)) {
      echo "&lt;font color='$ce'&gt;Fehler &lt;/font&gt;&lt;/br&gt;";
  } else {
      echo "&lt;font color='$cn'&gt;Kein Fehler &lt;/font&gt;&lt;/br&gt;";
  }
  </code></pre>