title: Replace two patterns at the same regex in JavaScript
body: <p>I need to replace one or two letters in a string in javascript but the letter is the same, then if I replace one of the two appareances the format is not correct:</p>
  <pre><code>HH:mm z [on] D MMM YYYY
  HH:mm zz [on] D MMM YYYY
  </code></pre>
  <p>In the first case in example z should be replaced by CEST and with zz by Central European Summer Time.</p>
  <p>I tried with regex but it is possible to replace the exact occurrence of first pattern without affecting to the second pattern?</p>