title: How to convert to schema.org JSON-LD duration with PHP
body: <p>duration in schema.org JSON-LD is in this format "duration": "PT4M5S" that it should be ISO-8601 
  but in PHP date('c') should return a string like this 2004-02-12T15:19:21+00:00 that it seems in a different format</p>
  
  <p>I have time in this format "00:03:06" and I need to get it in schema.org JSON-LD format, not sure if PHP has any way to do it</p>
  
  <p><a href="https://schema.org/duration" rel="nofollow noreferrer">https://schema.org/duration</a></p>