Non standard properties

X-PUBLISHED-TTL

The X-PUBLISHED-TTL property specifies a suggested iCalendar file download frequency for clients and servers with sync capabilities.

Use the setPublishedTTL() method with a ISO 8601-formatted string to set this duration.

use OpenCal\iCal\Domain\Entity\Calendar;

$calendar = new Calendar();
// set the duration to 2 hours
$calendar->setPublishedTTL(new DateInterval('PT2H'))