title: PHP Add n Minutes to Time/Date string and RETAIN timezone
body: <p>After an hour exploring Stack Overflow, I'm more confused than ever (and based on the number of posts, I'm probably missing something painfully obvious). All I want to do is add n minutes to an existing date/time string (formatted as $start = '2022-09-10T09:00:00-07:00') WITHOUT losing the time zone.</p>
  <p>Based on my reading, it looks like I need to use 'date' and 'strtotime' but when I do I lose the time zone. For example ...</p>
  <pre><code>$start = date('m:d:y H:i:s', strtotime($start . ' +90 minutes'));
  </code></pre>
  <p>...returns '09:10:22 14:30:00'</p>
  <p>When I try adding formatting like this to get the exact format I'm looking for...</p>
  <pre><code>$start = date(DATE_W3C, strtotime($start . ' +90 minutes'));
  </code></pre>
  <p>...it returns the correct format but changes the time zone: '2022-09-10T14:30:00+00:00'</p>
  <p>All I am trying to do is to take '2022-09-10T09:00:00-07:00'  and add 90 minutes to make it '2022-09-10T10:30:00-07:00'. What am I missing?</p>