title: How to create a custom DateTime in php?
body: <p>Hi here I have a scenario that i have two strings in two variables,</p>
  
  <pre><code>$a = '2017-03-09';
  $b = '16:00';
  </code></pre>
  
  <p>these are like date part and time part of <code>datetime</code> in <code>php</code>
  i want to join these part and create a <code>datetime</code>
  and want to perform <code>diff</code> operation , for example i have created this <code>datetime</code> as a variable <code>$custom_datetime</code></p>
  
  <p>my output should be as</p>
  
  <pre><code>$interval = $custom_datetime-&gt;diff(date());
  die($interval-&gt;format('%H:%I:%s'));
  </code></pre>
  
  <p>this operation should give a proper time difference but i am unable to make this <code>$custom_datetime</code></p>